JAHP_13_4_1016-1034

INTRODUCTION

Zinc (Zn) is one of the most extensively studied trace minerals in poultry nutrition owing to its vital function in maintaining health and productivity in production systems (Hu et al., 2024). The enhanced genetic capabilities of modern poultry breeds, along with challenges such as oxidative stress, high-density housing, and climate variability, have highlighted the importance of effective trace mineral management (Ao and Pierce, 2013). As nutritionists aim to refine feed formulations for optimal performance, Zn remains a key component because of its involvement in various metabolic activities and its ability to influence immune function, growth, and resilience in birds (Sahin et al., 2009).

Traditionally, poultry diets have relied on inorganic Zn sources, such as Zn sulfate and Zn oxide (ZnO), owing to their affordability and availability (Ezzati et al., 2013). However, these forms often demonstrate limited bioavailability and can interact negatively with other dietary components, leading to excessive supplementation and increased environmental Zn excretion. In contrast, organic Zn sources, such as Zn methionine, Zn proteinate, and amino acid chelates, have shown improved gastrointestinal stability and absorption (Abd El-Hack et al., 2017; Sahin et al., 2005; Suttle, 2022). More recently, Zn nanoparticles (NPs) have emerged, offering enhanced bio-efficacy at lower inclusion levels owing to their high surface area and better cellular uptake (Sukhanova et al., 2018; Wijnhoven et al., 2009). The National Research Council (NRC, 1994) recommends dietary Zn inclusion of 40–60 mg/kg for poultry, depending on age and physiological status. However, the efficacy of Zn supplementation depends largely on the chemical form of Zn used and its interactions with other nutrients in the diet (Hambidge, 2010; Lonnerdal, 2000).

The functions of Zn are closely related to those of other micronutrients. It enhances vitamin A metabolism by promoting retinol-binding protein synthesis (Gilbert et al., 2019; Rahman et al., 2002) and acts synergistically with vitamin E and selenium to regulate oxidative stress through the activation of antioxidant enzymes, such as superoxide dismutase and glutathione peroxidase (Aly and Mantawy, 2012; Marreiro et al., 2017). This synergism becomes especially critical under heat stress conditions, where oxidative damage, immune suppression, and reduced performance are common challenges. The Zn supplementation has been shown to alleviate the adverse effects of heat stress by enhancing antioxidant capacity, maintaining intestinal integrity, and supporting immune functions (Hu et al., 2025; Ren et al., 2025). These effects are further amplified when Zn is combined with other antioxidants, such as selenium and vitamin E (Bahrampour et al., 2021; De Grande et al., 2021). However, mineral interactions must be carefully managed, as high dietary levels of calcium, phosphorus, iron, and copper can inhibit Zn absorption through competitive transport mechanisms in the gut (Lonnerdal, 2000; Pang and Applegate, 2007; Spencer et al., 1984).

This review aims to critically evaluate the impact of different Zn sources and supplementation strategies on poultry nutrition. This highlights their comparative bioavailability, physiological roles, and gene-level effects, with a particular focus on the functional implications of Zn in immunity and birds under stress conditions.

Role of zinc in poultry

The Zn is a type-2 nutrient that is important for metabolism and is found throughout the body (King, 2011). The structure and catalytic activity of over 300 metalloenzymes are associated with Zn (Sanna et al., 2018). Zn plays a number of roles in poultry, which include (i) preserving normal growth, including the development of the skeleton and feathers as well as the health of the skin and foot; (ii) strengthening the immune system and preventing infectious diseases; (iii) changing the metabolism of proteins, lipids, and carbohydrates by increasing the activities of glutamic dehydrogenase, alcohol dehydrogenase, alkaline phosphatase, and RNA polymerase; (iv) boosting antioxidant capacities by increasing copper-Zn superoxide dismutase and zinc metalloenzyme activities; and (v) affecting gene expression by changing DNA and chromatin structure. By controlling the release of reproductive hormones during sexual maturation and protein synthesis in the epithelium during egg formation, dietary Zn supplementation improves egg production in layer and breeder birds (Figure 1) (Tabatabaie et al., 2007). Almost every signaling and metabolic pathway includes at least one Zn-dependent protein (Suttle, 2022). Additionally, adding Zn to the diet improves the immunological state of hens (Alirezaei et al., 2024) and the survival of their offspring when exposed to an Escherichia coli challenge (Virden et al., 2003). The Zn has been suggested to stimulate mineralization, bone production, and bone mass preservation (Mohd Yusof et al., 2022). It has been claimed that changes in the Zn status influence the expression of an array of genes via activation (Adam et al., 2024; Shi et al., 2020). Because of its role in gene regulation, it is necessary for the synthesis of several proteins. Two important structural proteins, keratin and collagen, require Zn (Suttle, 2022).

The Zn interacts with many nutrients, making it a potential key component of micronutrient malnutrition (Welch and Graham, 2012), including the intake, production, and metabolism of fatty acids, which influences the circulating lipid profile and may increase the risk of cardiovascular disease (Banaszak et al., 2021; Olechnowicz et al., 2018). Excessive Zn intake can limit the absorption of copper (Cu) and Fe, causing Cu deficiency and anemia, respectively (Stiles et al., 2024). The Zn is used as a supplement to alter the bird reproductive system, in addition to its role as a nutrient (Pereira et al., 2020; Prabakar et al., 2021). Zn lowers the negative impacts on the environment by reducing uricase activity in poultry litter to lower atmospheric ammonia emissions (Hunde et al., 2012). At physiological or appropriate levels, Zn acts as an antioxidant and protects against oxidative stress (Maret and Krężel, 2007; Özcelik et al., 2012). Metallothionein (MT) is a cysteine-rich, low-molecular-weight protein that regulates metal homeostasis and detoxifies the body. However, both Zn deficiency and excess impair MT function; low Zn lowers antioxidant defense, whereas high Zn increases MT expression but may have pro-oxidant effects by displacing other metals or affecting cellular redox signaling, resulting in oxidative stress under certain circumstances (Lee, 2018; Maret, 2019). Zinc has a synergistic antioxidant effect with both water-soluble (vitamin C) and fat-soluble (vitamin E) antioxidants (Maggini et al., 2017; Song et al., 2017).

Sources of dietary zinc

Inorganic zinc sources

The Zn can be derived from both organic and inorganic sources, with ongoing debate regarding the relative effectiveness of the two sources (Salama et al., 2003) (Figure 2). Zinc sulfate (ZnSO4) is favored as a source of Zn in poultry diets because of its cost-effectiveness and easy accessibility (Ezzati et al., 2013). Other inorganic sources include ZnO, Zn tetrabasic chloride, and Zn carbonate, which are used in the animal feed industry. Some researchers have suggested that the total amount of Zn in the diet should not exceed the NRC guidelines, which include Zn from natural components and mineral premixes. Although limiting dietary Zn according to NRC standards is favorable for the environment, it may not be optimum for certain physiological functions, and it is more critical when less bioavailable Zn sources are added to poultry diets (Burrell et al., 2004).

Organic zinc sources

Recent research has indicated that Zn from organic sources, such as Zn-methionine and Zn-propionate, is more bioavailable for production than Zn from ZnSO4 or Zn oxide (Abd El-Hack et al., 2017; Sahin et al., 2005). Based on the tibia mineral content, Zn from Zn-methionine or Zn-propionate is more bioavailable than Zn from inorganic sources (Rahman et al., 2002; Wedekind et al., 1992). The efficiency of Zn is determined by its gastrointestinal absorption and bioavailability in the blood (Naz et al., 2016). Metal-specific amino acid complexes, metal-proteinates, metal-amino acid chelates, and metal-amino acid complexes are examples of organic mineral sources. Amino acids are coupled with soluble metal salts in a 1:1 molar ratio, which may encourage birds to use minerals more frequently (Burrell et al., 2004). The Zn picolinate is a good and highly absorbable supply; additional forms include citrate, gluconate, and acetate, whereas sulfate is poorly absorbed (Barrie et al., 1987). Jahanian and Yaghoubi (2010) reported similar results; they found that adding Zn-methionine or Zn-lysine to broiler diets increased Zn bioavailability. Its high bioavailability improves nutrient absorption and utilization in animals, resulting in lower amounts in feed and less excretion without impairing performance (Mohammadi et al., 2015).

Nano zinc sources

In recent years, nanotechnology and its related products have rapidly advanced in various scientific fields (Kandeel et al., 2022). The Zn-NPs have received considerable interest in this regard because nano-formulation particulates have distinct differentiating properties, such as size, shape, wide surface area, high surface activity, high catalytic efficiency, and strong adsorption ability (Wijnhoven et al., 2009). They are more likely to change the biological consequences caused by them than their bulk materials (Patra and Lalhriatpuii, 2020), and the total amount required also decreases (Sukhanova et al., 2018). The Zn-NPs have recently received considerable attention owing to their small particle size and improved surface activity (El-Bahr et al., 2020a; Mohd Yusof et al., 2019). Numerous studies attempting to learn more about the effects of Zn nanoparticle addition on poultry development rate, intestinal architecture, and immune response have used Zn-NPs because of their good biocompatibility, low cost, and minimum toxicity (Jiang et al., 2018).

Effect of zinc levels and sources on growth performance

Several studies have been conducted to determine the effect of Zn on broiler chicken BWG, FI, and FCR, with different Zn sources optimized at various supplementation amounts (Table 1). Zn deficiency in broiler chickens reduces feed consumption (Quarterman, 1968; Quarterman et al., 1969). Furthermore, high dietary Zn reduces FI and growth rates in livestock and poultry (Naz et al., 2016). There is a need to determine the ideal dosage for supplementation in poultry. According to previous studies, adding Zn to birds boosts their growth performance. Sarvari et al. (2015) reported that the addition of 0.01% ZnO to the diet significantly increased (P<0.05) BWG (2120 vs. 1973 g), FCR (1.9 vs. 1.96), and FI (4043 vs. 3870 g) in broilers at 42 days of age. Similarly, Sahraei et al. (2013) found that supplementing 100-200 ppm of Zn from Bioplex® Zn or ZnSO4 was more effective than control and ZnO in terms of FCR (1.3 vs 1.4) during the broiler grower phase. In Ross-308 broilers, the ZnO-NP (40 ppm) group had a higher (P < 0.001) FCR than the control, ZnO, and Zn-Lys groups. FI decreased linearly (P = 0.003) in Ross-308 broiler chickens when supplemented with Zn lysine (Zn-Lys), ZnO, and ZnO-NPs at a level of 40 ppm in four different groups, and Zn-NPs (40 ppm) improved (P<0.001) BWG compared to ZnO and Zn-Lys supplementation (Alian et al., 2023).

Table 1: Effect of Zn on growth performance.

Dose (ppm)	Effect	Reference
40 (Zinc oxide, zinc lysine, and nano zinc oxide)	FI decreased linearly, and BWG and FCR increased	(Alian et al., 2023)
40 (Nano zinc oxide and conventional zinc oxide)	No difference in FI, BWG was higher and positive effect on FCR in the nano-zinc group.	(Qu et al., 2023)
20, 40 and 60 (Nano-zinc) and 60 (Organic zinc)	No influence on FI, higher BWG was observed in 40 ppm during the finisher phase and significant change in FCR observed in nano-zinc (60 ppm).	(Mozhiarasi et al., 2023)
40 and 60 (Nano zinc oxide)	Increased FI, increased BWG at 40 ppm zinc, and better FCR than control	(Hatab et al., 2022)
2.5, 5, 10, 20 and 40 (Nano-zinc) and 40 (Inorganic zinc)	2.5 ppm improved FI, BWG and FCR	(Hussan et al., 2022)
24, 54, 84 and 114	No influence on FCR	(Zaghari et al., 2018)
0.01%	FI increased, and better FCR and BWG	(Sarvari et al., 2015)
30, 60, 90 and 120 (Nanoparticles)	Positive effect on FI, BWG and FCR	(Ahmadi et al., 2013)
3, 6, and pre-biotic (With or without)	No effect on FI, BWG and FCR in quail	(Abd El-Samee et al., 2013)
50, 75, 100 and 125	Positive effect on FI and BWG but on effect on FCR	(Ezzati et al., 2013)
20-140 (Inorganic)	No effect on FI, BWG and FCR	(Liao et al., 2013)
10, 20, 40, or 80 (Inorganic and chelate)	Better daily FI	(Liu et al., 2013)
100-200 (Inorganic and chelate)	Better FCR	(Sahraei et al., 2013)
10, 20 or 40 (Organic) and 10, 20, 40 or 100 (Inorganic)	No effect on FI, BWG and FCR	(Vieira et al., 2013)
40, 60, 80, or 100 (Inorganic and organic)	No effect on FI, BWG but better FCR in organic zinc treatment	(Yogesh et al., 2013)
20, 40, 60 and 80 (Organic and inorganic)	No effect on FI, BWG and FCR	(Anil et al., 2012)
40 (Organic)	No effect on FI, BWG and FCR	(Salim et al., 2012)
5, 10, 15, 20 and 40 (Organic or inorganic)	No difference in FI, BWG but better FCR	(Star et al., 2012)
100 and 150 (Organic or inorganic)	Higher FI, BWG and better FCR	(Sahraei et al., 2012)
140 (Inorganic and chelate)	Better FI, BWG in layer birds	(Idowu et al., 2011)
60, 120 or 180	Increased daily FI but no effect on BWG and FCR	(Liu et al., 2011)
20, 40 and 80	No effect on FI, BWG and FCR	(Salim et al., 2011)
60 and 90 (Inorganic and organic)	Better daily FI, BWG and improved FCR	(Feng et al., 2010)
40 (complexed zinc) and 80 (Inorganic)	Increase in weight gain and improved FCR	(Saenmahayak et al., 2010)

FI: Feed intake; BWG: Body weight gain; FCR: Feed conversion ratio.

Conversely, Liao et al. (2013) observed no significant influence (P>0.54) on BWG, FI, and FCR in broilers fed a corn-soya diet containing Zn (20-140 ppm) from ZnSO4. They suggested that the Zn content in the base diet was sufficient for proper broiler growth during the finishing phase of production. Similarly, Vieira et al. (2013) discovered that supplementing Zn at levels of 10, 20, or 40 ppm, whether from ZnSO4 or Mintrex® Zn, did not lead to any noticeable change in FI, FCR and BWG at any stage or over the entire duration of the experiment in broiler chickens. This could be attributed to potential Zn recycling through litter consumption or the initial Zn concentrations present in the basal diet, which contained 58, 46, 41, and 38 ppm of Zn in each respective growth phase. Zhang et al. (2018) conducted research on Ross 308 broiler chickens supplemented with ZnSO4 at 0, 20, 40, 60, 80, 100, or 120 ppm in the starter diet and 0, 16, 32, 48, 64, 80, or 96 ppm in the grower diet. The results showed that Zn supplementation had no effect (P>0.05) on BWG, FI, and FCR at 21 and 42 d of age. This could be linked to Zn availability and supplementation levels (Leeson and Summers, 2009). This could also be due to the presence of phytate and calcium, which have been shown to form an insoluble combination with Zn, limiting its absorption in the small intestine (Salim et al., 2008).

Mozhiarasi et al. (2023) reported that dietary supplementation with organic Zn (60 ppm) or ZnO-NPs (20, 40, 60 ppm) in Cobb-400 broilers had no significant effect (P>0.05) on FI throughout the trial. The BWG was unaffected during the pre-starter and starter phases, but supplementation with 40 ppm ZnO-NPs significantly (P<0.05) improved the BWG during the finisher and overall periods. For FCR, 20 ppm ZnO-NPs differed significantly (P<0.05) from organic Zn and higher ZnO-NP levels during the pre-starter phase, whereas no significant differences were observed among the groups during the starter, finisher, and overall phases. In contrast, Hussan et al. (2022) observed that supplementation of 2.5 ppm ZnO-NPs in Cobb-400 broilers significantly (P<0.05) improved FI, BWG, and FCR compared to higher levels of ZnO-NPs (5–40 ppm) and inorganic Zn (40 ppm). The authors attributed these effects to enhanced nutrient digestion, absorption, and higher Zn bioavailability in NPs form, highlighting 2.5 ppm ZnO-NPs as the optimal inclusion level. The BWG was considerably increased by adding Moringa oleifera leaf powder extract stabilized with Zn-NPs (2.0 and 3.0 cm³/L). The additive had no detrimental effects on feed efficiency, as evidenced by the lack of significant variations in FI and FCR between the treated and control groups (El-Abbasy et al., 2025).

An experiment was conducted by Lail et al. (2023) on broilers infected with Eimeria tenella and treated with 60 mg/kg ZnO-NPs. In addition to reducing oocyst shedding and the anti-coccidial index, ZnO-NPs considerably (P<0.05) enhanced the growth performance of the infected birds. One possible explanation for this could be that Zn improves the antioxidant capability of chickens. Similarly, Hatab et al. (2022) reported that supplementation with ZnO-NPs (40 and 60 ppm) significantly (P<0.05) increased FI and BWG and improved FCR in broiler chickens compared to the basal diet, with 40 ppm showing better effects on body weight gain than 60 ppm. Qu et al. (2023) demonstrated that Arbor Acres broilers supplemented with 40 ppm ZnO-NPs (21 and 82 nm) had significantly (P<0.05) higher final BWG and improved FCR compared to conventional ZnO, although no differences were observed in FI. Collectively, these findings suggest that the beneficial effects of Zn supplementation in broilers are mainly attributed to the source (ZnO-NPs vs. conventional/organic Zn), whereas particle size differences exert a negligible influence on performance parameters.

The use of 40 ppm Zn in broiler feed is recommended by the NRC (1994). Some researchers, including those cited in previous studies (Rossi et al., 2007; Salim et al., 2011, 2012), argue that this 40 ppm level is sufficient for optimal broiler growth, with no discernible benefits from increasing Zn levels in poultry diets. However, in broilers fed a corn-soya diet supplemented with Zn propionate (Zn-P), ZnSO4, or ZnO at varying levels (40, 60, 80, or 100 ppm), Yogesh et al. (2013) observed no significant (P>0.05) impact on FI and BWG up to 42 days of age. However, a lower FCR (P<0.05; 2.3 vs. 2.4) was observed in the Zn-P group than in the ZnSO4 and ZnO groups. Dibaiee-Nia et al. (2017) investigated the effects of a wheat-based diet supplemented with different levels of Zn (20, 40, 60, 80, and 100 mg/kg). There was a significant improvement (P<0.05) in FCR with Zn supplementation, and 60 mg/kg had the best FCR among other treatments.

Effect of zinc levels and sources on carcass characteristics

Responses to Zn supplementation in poultry can lead to considerable variations in the weight and yield of various organs (Table 2). These discrepancies may stem from the diverse carcass characteristics examined in different studies. Mohammadi et al. (2015) observed significant differences (P<0.05) in quantitative carcass traits among dietary treatments, which included both dry and wet basal diets supplemented with Zn (100 or 200 ppm) from ZnO-NPs. The dry control diet containing 200 ppm ZnO-NPs resulted in increased carcass weight percentages (60.7 vs. 55.5) compared to other dietary treatments. However, Zaghari et al. (2018) found that as Zn supplementation (ranging from 24 to 114 ppm) increased in corn-SBM diets already containing dietary Zn (24 ppm), carcass weights (2053 vs. 1917 g) and percentages (78 vs. 75) decreased

Table 2: Effect of Zn on carcass characteristics.

Dose (ppm)	Effect	Reference
20, 40 and 60 (Nano-zinc) and 60 (Organic zinc)	No effect on water holding capacity but significantly increased the dressing percentage and reduced the meat pH	(Mozhiarasi et al., 2023)
40 and 60 (Nano zinc oxide)	Carcass yield increased significantly and lower gizzard weight observed at 40 ppm	(Hatab et al., 2022)
2.5, 5, 10, 20 and 40 (Nano-zinc) and 40 (Inorganic zinc)	No difference in cook yield, WHC, meat pH, giblet organs, abdominal fat, and breast yield was observed	(Hussan et al., 2022)
100 or 200 (Nanoparticles)	Carcass weights percentages increased by dry control diet with 200 ppm zinc	(F. Mohammadi et al., 2015)
0.01%	No effect on the carcass, abdominal fat, heart, and liver	(Sarvari et al., 2015)
24, 54, 84 or 114	Carcass weights were decreased as zinc supplementation increased	(Zaghari et al., 2018)
100 and 200 (Organic, inorganic, and nano)	ZnO had a lower carcass percentage	(Selim et al., 2014)
30, 60, 90, or 120 (Nanoparticles)	No effect on supplementation	(Ahmadi et al., 2013)
40, 60, 80 or 100	No effect on dressed, eviscerated, and giblet organ weights	(Yogesh et al., 2013)
20, 40, 60, or 80 (Inorganic or organic)	No significant difference in the ready-to-cook yields and the liver weights	(Anil et al., 2012)
40 and 80	No effect on WHC	(Saenmahayak et al., 2012)
60, 120, or 180 (Organic, inorganic, or chelate)	No effect of zinc levels and sources	(Liu et al., 2011)
20, 40 and 80 (Organic)	WHC of the breast was increased	(Salim et al., 2011)

WHC: Water holding capacity.

(P<0.01). This lack of response could be attributed to the utilization of fiber and phytate sources in the corn-SBM diet. Eskandani et al. (2021) reported significant improvements in Zn content of breast muscle, breast meat lightness and redness indexes, as well as breast meat shear force and pH, when supplemented with 70 mg Zn amino acid complex and 30, 50, 70, and 90 mg Zn-NPs. However, 30 mg of Zn-NPs is recommended for supplementation in broilers to enhance quality. In contrast, Sevim et al. (2021) reported non-significant results of carcass and meat quality in broilers when supplemented the diet with inorganic Zn and Zn-NPs.

Mozhiarasi et al. (2023) found that broilers (Cobb-400) had no effect (P>0.05) on water holding capacity (WHC), but significantly increased (P<0.05) the dressing percentage and reduced the meat pH when supplemented with ZnO-NPs compared to inorganic and organic Zn. In contrast, Hussan et al. (2022) found no differences (P>0.05) in the cook, giblet organ, abdominal fat, or breast yield of Cobb-400 broilers at 42 d of age. No significant effect (P>0.05) was observed on the WHC and pH of meat when supplemented with ZnO-NPs (2.5, 5, 10, 20, and 40 ppm). Hatab et al. (2022) found that the carcass yield increased significantly (P<0.05) in the groups with supplemented ZnO-NPs than the control group. The highest carcass yield was observed in the 40 ppm ZnO-NP-treated group. A significantly lower (P<0.05) relative gizzard weight was observed in the 40 ppm ZnO-NP group than in the control group, but the 60 ppm ZnO-NP group showed no difference from the control group. No significant intergroup differences were observed in the heart weight of the broilers. Dong et al. (2023) supplemented methionine hydroxyl analog chelated Zn in broiler diets at a dose of 90 mg/kg in low-protein diets and found non-significant results regarding carcass and meat quality. In an experiment, Abd El-Hack et al. (2024) supplemented the basal diets with 0.2 and 0.4 mg Zn-NPs/kg diet and found significant improvement in carcass and meat quality. Treatment with 0.4 mg Zn-NPs/kg enhanced dressing percentage and meat quality.

The variability in the effects of dietary Zn on factors such as carcass characteristics in birds may be attributed to the initial Zn content in the base diet or the quantity and sources of Zn to be added.

Effect of zinc levels and sources on the weight of immune organs

Zinc plays a vital role in supporting cell proliferation, especially in the immune system, and influences both innate and acquired immune functions. Ebrahimnezhad et al. (2013) found that administering over 90 ppm of Zn from ZnO-NPs resulted in improved (P<0.05) bursa and thymus weights in broilers at 42 days of age compared to lower levels (30 and 60 ppm) and a control diet (Table 3).

Table 3: Effect of Zn on the weight of immune organs.

Dose (ppm)	Effect	Reference
40 and 60 (Nano-zinc)	Significantly increased the spleen, bursa, and thymus weights	(Hatab et al., 2023)
40 (Nano zinc oxide and conventional zinc oxide)	Spleen and thymus index were higher in nano-zinc groups	(Qu et al., 2023)
100 or 200 (Nanoparticles)	No difference among treatments on the weight of the spleen and bursa	(F. Mohammadi et al., 2015)
15 (Inorganic), 7.5 and 15 (Organic) and (0.3, 0.06 and 0.03 (Nano-Zn)	The higher weight of the spleen	(Sahoo et al., 2014)
Coccidiosis vaccine (With or without 40, 120, or 200 zinc)	Weights of the bursa and spleen were higher	(Sajadifar et al., 2013)
30, 60 and 90 (Nanoparticles)	Improved the weights of the bursa and thymus	(Ebrahimnezhad et al., 2013)
20, 40 or 60	The weight of the spleen and bursa were not influenced but liver weight was higher at 60 ppm in broiler breeders	(Soni et al., 2013)
40, 120 and 200	Increase in weight of bursa and spleen	(Sajadifar et al., 2011)
30, 60 and 90	Spleen, thymus, and bursa indexes were higher at 90 ppm of the starter diet	(Feng et al., 2010)

Moreover, Soni et al. (2013) determined that dietary treatments (20, 40, or 60 ppm Zn methionine) had no significant impact on spleen and bursa weights (P>0.05) in broiler breeders aged 32–48 weeks. However, liver weight (P<0.01) was higher in birds fed a 60-ppm Zn diet compared to the control group (29.8 ppm dietary Zn + 10.2 ppm ZnSO4) and lower supplementation levels. Similarly, Yusof et al. (2023) reported that supplementation with ZnO-NPs had no effect (P>0.05) on the barsa of Fabricius weight. However, an increase in the weight of the spleen and thymus was observed in groups supplemented with higher levels of ZnO-NPs (40, 70, and 100 mg/kg) compared to the control group (ZnO).

Qu et al. (2023) found that the Arbor Acres broilers fed diets containing 40 ppm ZnO-NPs and conventional ZnO had a higher (P<0.05) spleen index than the negative control group. The thymus index was higher (P<0.01) in the ZnO-NP-treated groups (82 and 21 nm) than in the negative control group, whereas the bursa of Fabricius index remained the same between the groups. Hatab et al. (2023) found that 40 and 60 ppm Zn from ZnO-NPs significantly increased the spleen, bursa, and thymus weights as compared to the un-supplemented group in the Ross-308 broiler chickens.

In a distinct study involving broiler chicks at 7 weeks of age, relatively higher bursa weights were achieved with 8 ppm of Zn supplementation than with higher Zn concentrations (up to 125 ppm). Mohammadi et al. (2015) reported no statistically significant differences (P>0.05) in weight indexes for the spleen and bursa of Fabricius among the experimental treatments during the broiler starter phase, which included two basal diets (one dry and one wet) supplemented with either 100 or 200 ppm of Zn from ZnO-NPs. The lack of distinction between dietary treatments may be attributed to the unique characteristics of ZnO-NPs, including high particle kinetics, reactivity, contact surface, and diet form (wet or dry).

El-Katcha et al. (2017) performed an experiment on broilers, supplemented the basal diet with organic zinc (60, 45, 30, or 15 ppm) and ZnO-NPs (60, 45, 30, or 15 ppm), and found significant improvement (P<0.05) in lymphoid organ weight. In contrast, Jain et al. (2021) found a non-significant (P>0.05) response in immune organs (bursa of Fabricius and spleen) when supplemented with organic (20 and 40 ppm) and inorganic Zn (40 ppm). However, the Zn treatments had higher weights of immune organs than the control.

Effect of zinc levels and sources on antibody titer

The reassessment of Zn requirements exceeds the growth-related criteria and encompasses immunity. Multiple studies have shown that Zn concentrations exceeding NRC (1994) recommendations are necessary to enhance both humoral and cellular immune responses. Ezzati et al. (2013) found that different Zn levels (ranging from 50 to 125 ppm) from ZnSO4 improved humoral immune responses against ND virus (P<0.05). For broilers, methods such as hemagglutination inhibition (HA), hemagglutination inhibition (HI) (8.4 compared to 6.1), and enzyme-linked immunosorbent assay (ELISA) (14800 compared to 9863) did not exhibit improvements with Zn levels exceeding 100 ppm (Table 4). Similarly, Jain et al. (2021) found significant (P>0.05) results for antibody titers (IgG) between all treatment groups. A significantly

Table 4: Effect of Zn on antibody titer.

Dose (ppm)	Effect	Reference
40 (Zinc oxide, zinc lysine, and nano-zinc oxide)	Total antibody titer increased in the zinc lysine and nano-zinc oxide groups	(Alian et al., 2023)
40 and 60 (Nano-zinc)	Antibodies against Newcastle disease virus and Sheep red blood cells increased	(Hatab et al., 2023)
30 (Organic or nanoparticles)	The increase in antibody titers and cellular immune response was higher	(Sahoo et al., 2014)
3 or 6 (With or without prebiotic)	Better humoral response in Japanese quails	(Abd El-Samee et al., 2013)
50, 75, 100 or 125	Humoral immune response against NDV was improved	(Ezzati et al., 2013)
20, 40 or 60	Higher primary antibody titers and cellular immunity in broiler breeder	(Soni et al., 2013)
40, 120, and 200 (With and without vaccine)	Increase in the antibody titers against NDV	(Sajadifar et al., 2013)
10, 20 or 40	No effect on antibody titers against Bovine serum albumin	(Vieira et al., 2013)
40, 60, 80 or 100	No effect on cellular and humoral immune response	(Yogesh et al., 2013)
40, 120 and 200	Higher antibody titers against NDV	(Sajadifar et al., 2011)
30, 60, 90 or 120	Concentrations of Ig-G and IgM were increased in the starter phase	(Feng et al., 2010)

NDV: Newcastle disease virus, Ig: Immunoglobin.

(P <0.05) higher concentration of plasma IgG was reported in organic (20 and 40 ppm) and inorganic Zn (40 ppm) as compared to the control. In contrast, Rezapour et al. (2024) found non-significant results (P>0.05) of antibody titer against Infectious Bursal Disease (IBD) and lower antibody titer was observed (P<0.05) against bronchitis when supplemented with organic zinc (40 mg/kg feed).

In the study conducted by Soni et al. (2013), breeders fed a diet supplemented with Zn methionine displayed higher (P<0.05) primary antibody titers (6.4 compared to 4.3) against SRBC than those fed a control diet containing 40 ppm of Zn (29.8 dietary + 10.2 ppm from ZnSO4). At 48 weeks of age, breeders consuming a diet containing 100 ppm Zn exhibited higher cellular immunity to PHA-P (291 compared to 166) than those consuming lower levels. According to Ma and Ali (2025), 90 mg/kg Zn methionine supplementation had a significant effect (P<0.05) on the immune response in broilers vaccinated against ND. In a study by Vieira et al. (2013), the supplementation of Zn (at levels of 10, 20, or 40 ppm) with either ZnSO4 or Mintrex® Zn had no effect on antibody titers against BSA in broilers. This discrepancy in results might be attributed to the specific antigens used in the different immune protocol trials. However, Anoh et al. (2025) reported that the supplementation of ZnO in water at a dose of 200 mg/L with vaccine significantly (P<0.05) increased the HI antibody titer against ND and IBD in broiler chickens.

Hatab et al. (2023) found that the antibodies produced against ND virus and SRBC increased in the ZnO-NPs (40 and 60 ppm) groups than the un-supplemented control group in Ross-308 broilers at all test times. Sahoo et al. (2014) found that birds fed a basal diet containing 30 ppm of dietary Zn, along with supplementation of Zn methionine or ZnO-NPs, exhibited higher antibody titers (8.67 compared to 5.5) against SRBC compared to birds fed the basal diet or ZnSO4. Additionally, at 42 d of age, the cellular immune response (P<0.05) to PHA-P injection was significantly greater (171 vs. 121) in birds fed diets supplemented with organic Zn and ZnO-NPs than in birds fed other diets. According to Alian et al. (2023), different dietary sources (Zn oxide, Zn lysine, and nano-Zn) at a concentration of 40 ppm did not affect (P=1.00) the antibody titer against the ND vaccine on day 23 compared to the control group. On day 35, the total antibody titer increased in the Zn-Lys and ZnO-NP groups.

The variations in immune responses observed in different studies could be attributed to the specific types of antigens (Pimentel et al., 1991) used in each study, such as sheep red blood cells, bovine serum albumin, ND, and PHA-P.

Effect of mutual supplementation of zinc with other minerals on growth, carcass characteristics, and immune functions

Growth performance

El-Husseiny et al. (2012) found that broilers fed diets containing 100 percent organic Zn and manganese (Mn) and 50 percent organic Cu exhibited higher (P<0.001) FI (3349 compared to 3125 g), BWG (1374 compared to 1179 g), and FCR (2.8 compared to 4.7) than those fed other combinations of organic minerals (Table 5). Similarly, Sunder et al. (2013) observed no effect on FI, BWG, or FCR

Table 5: Effect of interaction of Zn on growth, carcass characteristics, and immune functions when supplemented with other minerals.

Dose (ppm)	Effect	Reference
Growth performance
24, 54, 84, or 114 (Zinc) and 100, 200, or 300 FTU/kg (Phytase)	No effect on feed intake and weight gain	(Zaghari et al., 2018)
40 or 80 (Zinc) and Cr (0.5 or 1)	Better feed conversion ratio and FI in quail	(Rouhalamini et al., 2014)
37, 70, or 175 (Zinc) and 200, 400, and 600 (Vitamin C)	Higher FI and weight gain but lower FCR in heat stress	(Al-Masad, 2012)
50 or 100 (Zinc), 60 or 120 (Manganese), and 8 or 16 (Copper)	Improved FI, weight gain, and FCR	(El-Husseiny et al., 2012)
Carcass characteristics
50 or 100 (Zinc), 60 or 120 (Manganese), and 8 or 16 (Copper)	Improved dressing, liver, and breast percentages but decreased wings (%)	(El-Husseiny et al., 2012)
Zinc, Chromium and Selenium	Improved carcass characteristics	(Sobhi et al., 2020)
Immune functions
40, 80 and 160 (Zinc) and 60, 120 and 240 (Manganese)	Better antibody production but cellular immune response was not influenced	(Sunder et al., 2013)
37, 70, or 175 (Zinc) and 200, 400, and 600 (Vitamin C)	Higher spleen and bursa weights and total antibodies	(Al-Masad, 2012)
40, 80, and 120 (Zinc) and 35, 70, and 105 (Copper)	No interaction on immune organ weights and antibody responses	(Arshami et al., 2010)

FI: Feed intake, FCR: Feed conversion ratio

in broilers up to 35 days of age when various combinations of organic Zn and Mn were added to a corn-SBM basal diet. It was presumed that the mineral concentrations in the basal diet were adequate for optimal growth. However, Sherif et al. (2024) conducted an experiment to determine the effect of dietary supplementation of Chlorella vulgaris (1 g) with ZnO-NPs (40 ppm) and selenium (Se) NPs (0.3 ppm) on broiler chicken performance. The results showed that the ZnO-NPs performed better (P<0.05) with Chlorella vulgaris than the synergistic supplementation with Se-NPs in terms of BWG. However, FCR was better in the treatment with ZnO-NPs and Se-NPs with Chlorella vulgaris. Similarly, Santos et al. (2021) added hydroxy-chloride Zn (80, 100, and 120 ppm) and Cu (15 and 150 ppm) to broiler chicken diets. These findings indicate that on day 42, the FCR was higher for birds supplemented with Cu (150 ppm) in diets containing Zn (100 ppm). The effect of feeding broilers sulfate or hydroxy-chloride forms of Zn and Cu at 15 and 80 ppm Zn levels was examined by Olukosi et al. (2018). None of the growth performance responses exhibited a significant source × mineral level relationship. On the other hand, broiler chickens that received hydroxy-chloride Zn and Cu had higher FCR (P<0.05), while those who received lower Zn levels had higher BWG (P<0.01).

Al-Masad (2012) found that broilers fed diets containing Zn and vitamin C at ratios of 35:600 and 70:200 ppm, respectively, exhibited higher FI (P<0.05) (773 compared to 637 g) and BWG (1992 compared to 1601 g) than other combinations when exposed to heat stress conditions (40°C) during the finisher phase. At the 4th, 5th, or 6th weeks of age, Zaghari et al. (2018) observed no effect on FI or BWG when Zn was supplemented with phytase in a diet containing 24 ppm of dietary Zn. The lack of reaction could be linked to the use of fiber and phytate sources and the lower bioavailability of ZnO compared to other Zn sources. Franklin et al. (2022) performed experiment to check the commercial premixes provide trace minerals such as Zn, Mn, and Cu (inorganic, organic and hydroxy) at 40, 60 and 8 ppm dose, respectively. The results revealed that the use of hydroxy trace minerals in broiler diets can maintain broiler performance and significantly reduce the negative impact on the environment (P<0.05). In broilers exposed to the Eimeria challenge, Chen et al. (2022) discovered that Zn:Cu:Mn in mineral methionine hydroxy-analog bis-chelate form (40:10:50 ppm) enhanced growth performance in contrast to high levels of inorganic trace minerals. These benefits may be attributable, in part, to an improved immunological response to coccidiosis as a result of increased bioavailability and antioxidant capacity.

Carcass characteristics

El-Husseiny et al. (2012) enhanced a diet with 100% inorganic Zn, Mn, and Cu, or 50% or 100% organic mineral sources. The diet containing 50% of each mineral (Zn, Mn, and Cu) resulted in enhancements in dressing percentage, liver weight, and breast meat percentage, but caused a decrease in wing meat percentage compared to the diet containing inorganic supplementation. This combined supplementation showed no significant effect (P<0.001) on the heart, gizzard, thigh meat, inedible parts, eviscerated yield, and giblet percentages. Sobhi et al. (2020) experimented on the Ross-308 broiler chickens and discovered that those fed yeast-based Zn, Se, and Cr had increased carcass weight, dressing %, and breast and thigh yield (P<0.05) compared to the control group. In the case of Zn, a low level (80 mg/kg) of supplementation was sufficient to attain good carcass traits.

Kwiecień et al. (2016) studied the effects of dietary ZnO (100 mg kg−1) and Zn glycine chelate (25, 50, or 100 mg kg−1) supplementation on male broilers (Ross 308) and found a positive trend in the weight of breast, thigh, and drumstick muscles when organic Zn was introduced, especially at doses of 50 and 25 mg. Similarly, Santos et al. (2021) concluded that the interaction between hydroxy-chloride Zn (80, 100, and 120 ppm) and Cu (15 and 150 ppm) had no effects on carcass characteristics, except the abdominal fat % in Cobb 500 broiler chickens. However, Olukosi et al. (2018) conducted an experiment in broilers to investigate the effect of supplementation with sulfate or hydroxy-chloride forms of Zn and Cu at 15 and 80 ppm Zn levels. The study found no significant association between the source and level of meat yield. Broiler chicks receiving hydroxy-chloride Zn and Cu exhibited a higher breast yield percentage (P < 0.05) than those receiving sulfate Zn and Cu.

Immune functions

Sunder et al. (2013) observed that the interaction between Zn and Mn had a significant impact on spleen weights (P<0.05), showing an increase in spleen weights when 120 ppm Mn was combined with all levels of Zn supplementation. They also noted that the combination of 80 ppm Zn and 240 ppm Mn resulted in higher antibody production (P<0.05) against SRBC than the other combinations. However, the Zn: Mn combination did not significantly affect the cellular immune response to PHA-P. In contrast, Arshami et al. (2010) found no interaction between different Zn (40, 80, and 120 ppm) and Cu (35, 70, and 105 ppm) levels on the weights of immune organs or the primary and secondary antibody responses against SRBC at 42 days of age. Similarly, Jain et al. (2021) supplemented inorganic and organic Zn (40 mg/kg), inorganic and organic Se (0.30 mg/kg), and inorganic and organic chromium (Cr) (2 mg/kg of feed). The results showed a non-significant change in the weight of the immune organs (bursa of Fabricius and spleen). Rezapour et al. (2024) found non-significant results (P>0.05) of antibody titer against IBD and higher antibody titer was observed (P<0.05) against bronchitis when supplemented with organic Zn, Mn, and Cr (40 mg, 30mg, and 2mg/Kg feed, respectively) than the other treatments.

Al-Masad (2012) discovered that supplementing combinations of Zn and vitamin C in the diet of heat-stressed birds (40 ºC) during the finisher phase led to increased spleen and bursa weights (P<0.05), as well as higher primary antibody responses for IgG, IgM, and total antibodies (4.65 vs 2.05), and secondary antibody responses for IgG, IgM, and total antibodies. Similar results were reported by Faghih-Mohammadi et al. (2023), when chelated forms of Zn, Cu, iron, manganese, and Se were added at 110, 10, 50, 120, and 0.3 mg kg− 1 in broiler breeder chicken diets. There was improvement in immune system of broilers fed experimental diets containing chelated forms of Zn, Fe, Cu, Se, and Mn and a basal diet containing 50% of the minerals Zn, Fe, Cu, Se, and Mn in the sulfate form and 50% in the chelate form. In contrast, Jankowski et al. (2019) examined the efficacy of feeding turkeys a combination of Cu (2 and 20 mg), Zn (10 and 100 mg), and Mn (10 and 10 mg) NPs. The study demonstrated that the antioxidant and immunological defense of turkeys was unaffected by the addition of Cu, Zn, and Mn to their diets in conventional forms and as NPs at 2, 10, and 10 mg Cu, Zn, and Mn, respectively. Likewise, a lack of additional Cu, Zn, and Mn in the turkey diet did not significantly influence immunity and even lowered the quantity of MDA in the small intestine and liver. Alterations in the redox status of turkeys whose diets were not supplemented with Cu, Zn, or Mn could imply decreased oxidation processes in the tissues.

Effect of zinc supplementation on growth, carcass characteristics, and immune functions in a hot environment

Growth performance

The Zn was recognized for its potential to alleviate the negative effects of heat stress in animals, although there are inconsistencies in the available evidence supporting this particular role of Zn. Salabi et al. (2011) observed that broilers provided with a diet containing 90 ppm of Zn displayed higher levels of FI (4481 vs 4417 g), BWG (2459 vs 2370 g), and an improved FCR of 1.82 compared to broilers on a diet with adequate Zn (45 ppm of Zn) at 42 days of age (Table 6). Similarly, Zhu et al. (2017) reported that supplementation of 110 mg/kg of Zn as either inorganic or organic Zn in the maternal diet alleviated the negative effect of maternal heat stress (32 ± 1°C) on the growth performance of offspring during the starter period. In a study, Waeothong et al. (2021) found that the supplementation of ZnO (40 ppm) and ZnSO4 (40, 500 and 1000 ppm) improved the performance of the broiler chickens under heat stress (30 °C), and suggested 40 ppm Zn, an optimal dose for the supplementation.

Table 6: Effect of Zn supplementation on growth, carcass characteristics, and immune functions in a hot environment.

Dose (ppm)	Effect	Reference
Growth performance
40 or 80	Linearly improved the feed conversion ratio in quails	(Rouhalamini et al., 2014)
45, 90 and 135	Improved feed intake, weight gain, and feed conversion ratio	(Salabi et al., 2011)
Carcass characteristics
40 or 80	Increased the pH and water-holding capacity of meats in quails	(Rouhalamini et al., 2014)
3 or 6 (Organic with or without prebiotic)	No influence on the carcass, liver, gizzard, alimentary canal, and heart weights in quails	(Abd EL Samee et al., 2013)
45, 90 or 135	No influence on breast and thigh meat yields	(Salabi et al., 2011)
Immune functions
40 or 80	No effect on the weights of the spleen, bursa, and thymus in quails	(Rouhalamini et al., 2014)
3 or 6 (With or without prebiotic)	No influence on the bursa of Fabricius, thymus, spleen, and thyroid gland weights in quails	(Abd EL Samee et al., 2013)
45, 90 and 135	Heavier bursa but liver weight was decreased and spleen weight was not affected	(Salabi et al., 2011)

Conversely, Zaghari et al. (2022) revealed that supplementing the diet with HiZox® (75, 100, and 125 ppm of Zn) or ZnO (100 ppm of Zn) had no significant effect on BWG and FI in broilers under heat stress. However, heat-stressed broilers receiving different dosages of HiZox® had 2.85% lower mortality than the normal ZnO group (P<0.06).

Rouhalamini et al. (2014) discovered that quails receiving diets supplemented with 40 ppm of Zn and 1 ppm of Cr had an improved FCR (2.6 vs 3.2) compared to other combinations. Moreover, when both minerals were supplemented together, quails exhibited better intake than when each mineral was fed separately. They also found that providing Zn to Japanese quails in a heat-stressed environment led to an improved FCR compared to diets without Zn supplementation. Al-Masad (2012) also reported that heat-stressed broilers fed diets with Zn: vitamin C ratios of 70:200 ppm and 35:400 ppm had a lower FCR (2.4 vs. 3.1) than those fed control diets and other combinations during the finisher phase. Ramiah et al. (2019) found lower FI and FCR in the broiler chickens fed 100 ppm ZnO-NPs under heat stress (34 ± 1°C) than the control from 1 to 42 day of experimental trial. Shah et al. (2018) performed an experiment on the broiler chicken and observed that the supplementation of Zn (30 and 60 mg ZnSO4) singly or in combination with probiotic improved (P<0.05) the BWG and FCR in the heat stressed birds. In a study by Saleh et al. (2018), Zn methionine (25, 50, and 100 mg/kg) supplementation considerably improved broiler growth performance by increasing BWG and FCR (P<0.05) at high ambient temperature. One possible explanation for such benefits could be that Zn is crucial in maintaining the structure of metalloproteins such as IGF-1 (Khan et al., 2014; Saleh et al., 2012).

Carcass characteristics

Rouhalamini et al. (2014) noted that supplementing Zn (40 or 80 ppm) resulted in an elevation of pH (5.50 vs 5.25) and WHC (65.6 vs 63.1 percent) in the meat of Japanese quails in the heat-stressed environment. Conversely, Akhavan-Salamat and Ghasemi (2019) reported that the ZnO, Zn methionine, and ZnO-NPs at 20, 40, and 80 mg/kg had no effect on the carcass traits of the male broiler chickens (Ross 308) under heat stress. De Grande et al. (2022) conducted an experiment to examine the effect of Zn (60 ppm organic or inorganic) and vitamin E (50 or 100 IU/kg) supplementation on broilers under heat stress. The results revealed that organic Zn can improve breast meat yield and increase the WHC of broiler breast meat under chronic cyclic heat stress compared to inorganic Zn. Furthermore, the beneficial effects of organic Zn on breast meat yield and quality appear to be independent of vitamin E. Abd El-Samee et al. (2013) also found that supplementing organic Zn with or without prebiotics in the diet of heat-stressed Japanese quails (heat-stressed) did not influence carcass, liver, gizzard, alimentary canal, and heart weights. It is worth noting that in this study, both the temperature and humidity levels were higher, which could explain the absence of a performance response. Similarly, Zhu et al. (2017) observed non-significant results for carcass characteristics in broiler offspring when breeder hens were supplemented with 110 mg/kg Zn (inorganic and organic Zn). However, progeny meat quality improved due to organic Zn supplementation in the maternal diet. The non-significant results in carcass characteristics showed that Zn supplementation reduced the heat stress effect in the progeny.

Immune functions

Salabi et al. (2011) noted that broilers receiving diets containing 135 ppm of Zn from ZnSO4 had a higher bursa weight (0.15 vs 0.12 percent of body weight) compared to heat-stressed broilers fed diets with 45 and 90 ppm of Zn. As Zn levels in the diet increased, liver weight decreased (P<0.05), whereas spleen weight remained unchanged. The reduction in liver weight might be attributed to decreased FI, leading to fewer nutrients available for liver and spleen growth. Abd El-Samee et al. (2013) reported that supplementing organic Zn with or without prebiotic in a basal diet during the growing phase of Japanese quails under heat stress did not affect the weights of the bursa of Fabricius, thyroid gland, spleen, and thymus. Notably, both the humidity and temperature were higher in this study, which could explain the absence of a performance response. However, Akhavan-Salamat and Ghasemi (2019) observed that delivering Zn in the form of Zn methionine and ZnO-NP at a dose of 40 mg/kg of feed could improve the immunological response and antioxidant status of broiler chickens grown under high ambient temperatures.

Hu et al. (2024) the author stated that supplementation with organic and inorganic Zn (30, 60, and 90 ppm) significantly enhanced serum antioxidant levels in Xueshan hens, with better superoxide dismutase and glutathione peroxidase activities, and that organic Zn was more efficient than inorganic Zn. However, Rouhalamini et al. (2014) found that Zn supplementation (40 or 80 ppm) had no effect on the weights of the thymus, bursa, and spleen in Japanese quails under heat stress. However, Shah et al. (2018) observed that that the supplementation of Zn (30 and 60 mg ZnSO4) singly or in combination with probiotic increased (P<0.05) the area of cecal tonsils and bursa of Fabricius in the heat stressed birds (35± 1 °C). Ramiah et al. (2019) conducted a heat stress experiment on broiler chickens and proposed supplementation with 40 and 60 ppm ZnO-NPs to reduce corticosterone levels, which could be linked to Zn’s antioxidant and antistress ability.

Effect of zinc supplementation on gene expression

Zn is a trace element that plays crucial roles in gene transcription, DNA synthesis, gene expression, RNA synthesis, and cellular division (Prasad, 1991). Sahin et al. (2009) emphasized its significance in poultry diets for mitigating the effects of heat stress. There is limited scientific literature on the impact of ZnO-NPs on poultry performance under heat stress conditions. Ramiah et al. (2020) found that supplementation of Zn-NPs increased mRNA levels of ghrelin and cholecystokinin in the gut (Table 7). In comparison to regular ZnO, dietary ZnO-NPs significantly elevated IgG and ghrelin levels in aged layers (Mao and Lien, 2017). Hu et al. (2016) reported that broiler chickens receiving Zn supplements exhibited

Table 7: Effect of Zn supplementation on gene expression.

Dose (ppm)	Effect	Reference
40 (Zinc oxide, zinc lysine, and nano-zinc oxide)	Nano-zinc increased mRNA expression of insulin-like growth factor-I in the liver tissues	(Alian et al., 2023)
100 and 130	Improved the tight junction protein expression	(Barzegar et al., 2022)
15, 30 and 60	Upregulated the levels of antioxidant enzymes and pro-inflammatory cytokines in quails	(El-Bahr et al., 2020b)
40 and 80	Increased the activity of superoxide dismutase and catalase but decreased the concentration of malondialdehyde	(Hafez et al., 2020)
40, 60 and 100	Altered the gene expression of ghrelin, heat shock protein-70, heat shock protein-90, and cholecystokinin	(Ramiah et al., 2020)
40, 60 and 100	Raised the serum corticosterone levels	(Ramiah et al., 2019)
15, 30, 60, 120, and 240	Increased the tight junction protein and mRNA levels of barrier-related genes in pekin ducks	(Wen et al., 2018)
50 (Organic and nano-ZnO)	Influenced the levels of MDA, SOD, and mRNA expression of growth hormones and insulin	(Ibrahim et al., 2017)
80 (Organic, inorganic and nanosized)	Nano-zinc increased immunoglobin-G and ghrelin level in brown laying hens	(Mao and Lien, 2017)
120	Reduced ghrelin mRNA expression	(Hu et al., 2016)
20, 70 and 320	Decreased tumor necrosis factor-α and active A20 abundance in broiler breeder	(Li et al., 2015)
30, 60, 90 or 120 (Nanosized)	Lower levels of MDA and higher levels of SOD and CAT	(Ahmadi et al., 2014)
20, 60 and 100 (Nanosized)	Lower levels of MDA and higher levels of SOD but no effect on CAT	(Zhao et al., 2014)

SOD: Superoxide dismutase, MDA: Malondialdehyde, CAT: Catalase

reduced ghrelin mRNA expression in hypothalamic tissue. Broiler chickens receiving the highest levels of ZnO-NPs showed increased levels of heat shock protein 90 mRNA expression in the glandular stomach and duodenal tissue samples (Ramiah et al., 2020). Same findings were reported by Ramiah et al. (2019), who showed that a feed containing 100 ppm ZnO-NPs increased serum corticosterone levels. Dietary ZnO-NPs altered the expression of genes for heat shock protein 70 (in the jejunum and ileum), cholecystokinin (in the ileum), and heat shock protein 90 (duodenum, jejunum, and ileum). The interaction between temperature and ZnO-NPs concentration in the duodenum and stomach affected the expression of ghrelin (Ramiah et al., 2020).

Chickens fed diets containing ZnO-NPs displayed decreased malondialdehyde levels and increased superoxide dismutase and catalase activity. Zn also influences the mRNA expression of growth hormone and insulin genes (Ahmadi et al., 2014; Ibrahim et al., 2017; Zhao et al., 2014). In Japanese quails, all tested doses of ZnO-NPs significantly elevated the mRNA levels of superoxide dismutase 1, catalase, glutathione peroxidase 1, interleukin 6, and interferon alpha genes in the liver and brain tissues compared to the control. However, the expression of glutathione peroxidase-7 in the brain tissue remained unchanged in Japanese quails in the control group fed ZnO-NPs (El-Bahr et al., 2020). The antioxidant impact of ZnO-NPs in Japanese quail liver and brain tissues was confirmed at the molecular level, with a notable increase in antioxidant enzyme genes (superoxide dismutase 1, catalase, and glutathione peroxidase 1). Broilers supplemented with ZnO-NPs exhibited significantly increased antioxidant enzymes, superoxide dismutase, and catalase activity, along with reduced malondialdehyde concentration (Hafez et al., 2020).

Supplementation with either small or large ZnO (100 and 130 ppm) improved the expression of tight junction proteins zonula occludens-1 and occludin, reducing intestinal inflammation (decreased tumor necrosis factor) in breeder chickens (Ross-308) (Barzegar et al., 2022). Wen et al. (2018) experimented on ducks and found that Zn added to diets increased (P<0.05) the transcription of tight junction proteins claudin1, occludin, zonula occludens-1, and zonula occludens-3 in the jejunum. The mRNA levels of claudin2 (leak protein) decreased with increasing dietary Zn levels at 14 and 35 days of age. Zn supplementation increased (P<0.05) the mRNA levels of the chemical barrier-related genes mucin2 and trefoil factor-2 in the jejunum at 14 and 35 days of age, as well as the transcription of immunological barrier-related genes immunoglobin A, polymeric immunoglobulin receptor, lysozyme, and avian β-defensin 2. Environmental conditions, such as intestinal infections, low-quality feed ingredients, and variations in feed formulation, can induce gut inflammation during commercial production (Kogut et al., 2018). The innate immune system triggers inflammation in response to infection, potentially harmful chemicals, and host damage. This leads to the synthesis of various cells and pro-inflammatory molecules, such as tumor necrosis factor (Barton, 2008). Stress may increase the expression of pro-inflammatory cytokines, but the harmful effects of inflammation can be mitigated by anti-inflammatory substances such as Zn (Barzegar et al., 2022). Zn has been shown to shield cells from tumor necrosis factor α-induced breakdown of the monolayer cell layer (Hennig et al., 1993). Increased Zn levels in the diet reduce the number of inflammatory components in hens susceptible to intestinal inflammation due to once daily feeding (Barzegar et al., 2022). Alian et al. (2023) discovered that the ZnO-NPs at the concentration of 40 ppm linearly increased (P<0.001) the mRNA expression of IGF-I in the liver tissues of Ross-308 broiler chickens as compared to the ZnO, Zn-Lys, and control (un-supplemented) groups.

Research suggests that adding Zn to the diet of broiler breeders can enhance the intestinal morphological traits of offspring by causing DNA hypomethylation and hyperacetylation of histone H3 at lysine 9 (H3K9) at the A20 promoter region. Organic Zn added to the mothers’ diet showed greater attenuation of gut impairment but decreased tumor necrosis factor-α and active A20 abundance compared to inorganic Zn (Li et al., 2015).

CONCLUSION

This review concludes that Zn supplementation in poultry diets can enhance growth performance, health status, and meat quality. The bioavailability of Zn-NPs form surpasses that of conventional Zn sources, both organic and inorganic, likely due to its size, availability, and absorption characteristics. Furthermore, Zn from organic sources exhibits greater bioavailability than Zn from inorganic sources. Dietary Zn sources significantly influence gene expression and the management of heat stress, and they can be effectively combined with other minerals to improve performance. Zinc supplementation bolsters the immune system of birds, potentially by increasing the weights of immune organs. Additionally, Zn enhances the absorptive capacity of the small intestine in poultry. This review also highlights Zn’s role in protecting cells against free radical damage, suggesting its inclusion in poultry feed to mitigate oxidative stress. Although the exact way Zn benefits poultry is not fully understood, it is thought to improve gut metabolism and enzyme activity, support feed intake and nutrient use, strengthen gut immunity, and boost antioxidant enzyme production. However, existing literature presents conflicting findings regarding the effects of Zn supplementation on performance, health, and meat quality in birds, necessitating further investigation. These discrepancies may arise from variables such as chicken age, sex, breed, broiler strains, dietary Zn content, environmental factors, and rearing conditions.

ACKNOWLEDGMENTS

We would like to express our sincere gratitude to Institute of Animal and Dairy Sciences, University of Agriculture, Faisalabad.

Novelty Statement

This review highlights the supplemental effect of different sources and levels of Zinc in poultry birds. The importance of Zinc in growth performance, health, quality and immunity under stress conditions and at genetic level.

AUTHOR’S CONTRIBUTION

MA, MS and SH: Wrote the manuscript.

MMAH and WA: Edited the final version of the manuscript.

HT and MIS: Prepared the figures and tables of the manuscript.

SH: Correspondence.

All authors contributed to the revision of the manuscript, intellectual content, and approved the manuscript for publication.

Generative AI and AI-assisted technology statement

The authors declare the use of AI in enhancing the writeup of the content. AI was employed ethically to improve quality and transparency while respecting academic standards.

Conflict of interest

The authors have declared no conflict of interest.

REFERENCES

Abd El-Samee DL, El-Wardany I, Nematallah GA, Abo Elaom (2013). Effect of dietary organic zinc and prebiotic on productive performance and immune response of growing quails. Iran. J. Appl. Anim. Sci., 3(4): 761-767.

Abd El-Hack ME, Alagawany M, Arif M, Chaudhry MT, Emam M, Patra A (2017). Organic or inorganic zinc in poultry nutrition: A review. Worlds Poult. Sci. J., 73(4): 904–915. https://doi.org/10.1017/S0043933917000769

Abd El-Hack ME, Ashour EA, Aljahdali N, Zabermawi NM, Baset SA, Kamal M, Radhi KS, Moustafa M, Algopishi U, Alshaharni MO (2024). Does the dietary supplementation of organic nano-zinc as a growth promoter impact broiler’s growth, carcass and meat quality traits, blood metabolites and cecal microbiota? Poult. Sci., 103(5): 103550. https://doi.org/10.1016/j.psj.2024.103550

Adam SY, Muniyappan M, Huang H, Ennab W, Liu H-Y, Ahmed AA, Sun M, Dessie T, Kim IH, Hu Y (2024). Dietary organic zinc Supplementation modifies the oxidative genes via RORγ and epigenetic regulations in the Ileum of broiler chickens exposed to high-temperature Stress. Antioxidants, 13(9): 1079. https://doi.org/10.3390/antiox13091079

Ahmadi F, Ebrahimnezhad Y, Sis NM, Ghiasi J (2013). The effects of zinc oxide nanoparticles on performance, digestive organs and serum lipid concentrations in broiler chickens during starter period. Int. J. Biosci., 3(7): 23–29. https://doi.org/10.12692/ijb/3.7.23-29

Ahmadi F, Ebrahimnezjad Y, Ghalehkandi JG, Sis NM (2014). The effect of dietary zinc oxide nanoparticles on the antioxidant state and serum enzymes activity in broiler chickens during starter stage. In: International conference on biological, civil and environmental engineering, Dubai, pp. 26–28.

Akhavan-Salamat H, Ghasemi HA (2019). Effect of different sources and contents of zinc on growth performance, carcass characteristics, humoral immunity and antioxidant status of broiler chickens exposed to high environmental temperatures. Livest. Sci., 223: 76–83. https://doi.org/10.1016/j.livsci.2019.03.008

Alian HA, Samy HM, Ibrahim MT, Yusuf MS, Mahmoud MMA (2023). Nano zinc oxide improves performance, IGF-I mRNA expression, meat quality, and humeral immune response and alleviates oxidative stress and NF-κB immunohistochemistry of broiler chickens. Biol. Trace Elem. Res., 201(8): 4062–4078. https://doi.org/10.1007/s12011-022-03494-y

Alirezaei Shahraki P, Kheiri F, Amanlou H, Faghani M, Jalali SMA (2024). Determining the optimal level and the effect of different zinc sources on performance, egg quality and the immune system of laying hens at the end of the production period. Vet. Med. Sci., 10(5): e70035. https://doi.org/10.1002/vms3.70035

Al-Masad M (2012). Effects of vitamin C and zinc on broilers performance of immunocompetence under heat stress. Asian J. Anim. Sci., 6(2): 76–84. https://doi.org/10.3923/ajas.2012.76.84

Aly HF, Mantawy MM (2012). Comparative effects of zinc, selenium and vitamin E or their combination on carbohydrate metabolizing enzymes and oxidative stress in streptozotocin induced-diabetic rats. Eur. Rev. Med. Pharmacol. Sci., 16(1).

Anil KC, Ramana J V, Rama PJ, Sudheer SD, Satyanarayana R (2012). Influence of zinc sulphate and zinc-methionine dietary supplementation on carcass characteristics and feed efficiency of broilers. Ann. Biol. Res., 3(8): 4215–4221.

Anoh KU, Ozung PO, Evans EI (2025). Aspects of the physiological response of vaccinated and unvaccinated broiler chickens administered zinc oxide as a supplement. Anim. Res. Int., 22(1): 5952–5960.

Ao T, Pierce J (2013). The replacement of inorganic mineral salts with mineral proteinates in poultry diets. Worlds. Poult. Sci. J., 69(1): 5–16. https://doi.org/10.1017/S0043933913000019

Arshami J, Hosseini S, Torshizi ME (2010). Immunomodulatory effects of graded copper and zinc on SRBC titer and lymphoid organs in broiler chicks. J. Anim. Vet. Adv., 9(10): 1510–1514. https://doi.org/10.3923/javaa.2010.1510.1514

Bahrampour K, Ziaei N, Esmaeilipour OA (2021). Feeding nano particles of vitamin C and zinc oxide: Effect on growth performance, immune response, intestinal morphology and blood constituents in heat stressed broiler chickens. Livest. Sci., 253: 104719. https://doi.org/10.1016/j.livsci.2021.104719

Banaszak M, Górna I, Przysławski J (2021). Zinc and the innovative zinc-α2-glycoprotein adipokine play an important role in lipid metabolism: A critical review. Nutrients, 13(6): 2023. https://doi.org/10.3390/nu13062023

Barrie SA, Wright J V, Pizzorno JE, Kutter E, Barron PC (1987). Comparative absorption of zinc picolinate, zinc citrate and zinc gluconate in humans. Agents Actions, 21(1): 223–228. https://doi.org/10.1007/BF01974946

Barton GM (2008). A calculated response: control of inflammation by the innate immune system. J. Clin. Invest., 118(2): 413–420. https://doi.org/10.1172/JCI34431

Barzegar M, Zaghari M, Zhandi M, Sadeghi M (2022). Effects of zinc dosage and particle size on gut morphology, tight junctions and TNF-α expression in broiler breeder hens. J. Anim. Physiol. Anim. Nutr. (Berl)., 106(4): 772–782. https://doi.org/10.1111/jpn.13638

Burrell AL, Dozier WA, Davis AJ, Compton MM, Freeman ME, Vendrell PF, Ward TL (2004). Responses of broilers to dietary zinc concentrations and sources in relation to environmental implications. Br. Poult. Sci., 45(2): 225–263. https://doi.org/10.1080/00071660410001715867

Chen J, Yan F, Kuttappan VA, Cook K, Buresh B, Roux M, Hancock D, Vázquez-Añón M (2022). Effect of methionine and trace minerals (zinc, copper and manganese) supplementation on growth performance of broilers subjected to Eimeria challenge. Front. Physiol., 13: 991320. https://doi.org/10.3389/fphys.2022.991320

De Grande A, Ducatelle R, Delezie E, Rapp C, De Smet S, Michiels J, Haesebrouck F, Van Immerseel F, Leleu S (2021). Effect of vitamin E level and dietary zinc source on performance and intestinal health parameters in male broilers exposed to a temperature challenge in the finisher period. J. Anim. Physiol. Anim. Nutr. (Berl)., 105(4): 777–786. https://doi.org/10.1111/jpn.13492

De Grande A, Ducatelle R, Leleu S, Rapp C, Torres C, Petracci M, De Smet S, Michiels J, Haesebrouck F, Van Immerseel F (2022). Effects of the dietary zinc source and vitamin E level on live weight and carcass yield and meat quality in male broilers reared under chronic cyclic heat stress conditions in the finisher phase. Front. Physiol., 13: 992689. https://doi.org/10.3389/fphys.2022.992689

Dibaiee-Nia G, Akbari MR, Karimi S (2017). Effects of supplemental zinc in a wheat-based diet on performance, intestinal viscosity, immune system and lipid peroxidation of 21-day old broiler chickens. Poult. Sci. J. 5 (1): 7-15.

Dong L, Li Y, Zhang Yonghong, Zhang Yan, Ren J, Zheng J, Diao J, Ni H, Yin Y, Sun R (2023). Effects of organic zinc on production performance, meat quality, apparent nutrient digestibility and gut microbiota of broilers fed low-protein diets. Sci. Rep., 13(1): 10803. https://doi.org/10.1038/s41598-023-37867-7

Ebrahimnezhad Y, Gheiasi J, Maheri N, Mohammadikhah M, Ahmadi F (2013). Influence of zinc oxide nanoparticles on growth performance, carcass quality and growth index of immune organs of broiler chickens. Poult. Sci., 92: 98–107.

El-Abbasy MM, Aldhalmi AK, Ashour EA, Bassiony SS, Kamal M, Alqhtani AH, Abou-Kassem DE, Elolimy AA, Abd El-Hack ME, Swelum AA (2025). Enhancing broiler growth and carcass quality: Impact of diets enriched with Moringa oleifera leaf powder conjugated with zinc nanoparticles. Poult. Sci., 104(1): 104519. https://doi.org/10.1016/j.psj.2024.104519

El-Bahr SM, Shousha S, Albokhadaim I, Shehab A, Khattab W, Ahmed-Farid O, El-Garhy O, Abdelgawad A, El-Naggar M, Moustafa M (2020). Impact of dietary zinc oxide nanoparticles on selected serum biomarkers, lipid peroxidation and tissue gene expression of antioxidant enzymes and cytokines in Japanese quail. BMC Vet. Res., 16(1): 1–12. https://doi.org/10.1186/s12917-020-02482-5

El-Husseiny OM, Hashish SM, Ali RA, Arafa SA, Abd El-Samee LD, Olemy AA (2012). Effects of feeding organic zinc, manganese and copper on broiler growth, carcass characteristics, bone quality and mineral content in bone, liver and excreta. Int. J. Poult. Sci., 11(6): 368. https://doi.org/10.3923/ijps.2012.368.377

El-Katcha M, Soltan MA, El-Badry M (2017). Effect of dietary replacement of inorganic zinc by organic or nanoparticles sources on growth performance, immune response and intestinal histopathology of broiler chicken. Alex. J. Vet. Sci., 55(2). https://doi.org/10.5455/ajvs.266925

Eskandani M, Janmohammadi H, Mirghelenj SA, Ebrahimi M, Kalanaky S (2021). Effects of zinc nanoparticles on growth performance, carcass characteristics, immunity, and meat quality of broiler chickens. Iran. J. Appl. Anim. Sci., 11(1).

Ezzati MS, Bozorgmehrifard MH, Bijanzad P, Rasoulinezhad S, Moomivand H, Faramarzi S, Ghaedi A, Ghabel H, Stabraghi E (2013). Effects of different levels of zinc supplementation on broilers performance and immunity response to Newcastle disease vaccine. Eur. J. Exp. Biol., 3(5): 497–501.

Faghih-Mohammadi F, Seidavi A, Bouyeh M (2023). Effects of the dietary chelated form of trace minerals on hatchability, immune system response, blood constitutes, and estrogen hormone in ross 308 broiler breeders. Biologia (Bratisl)., 78(12): 3427–3439. https://doi.org/10.1007/s11756-023-01480-w

Feng JWQM, Ma WQ, Niu HH, Wu XM, Wang Y, Feng J (2010). Effects of zinc glycine chelate on growth, hematological, and immunological characteristics in broilers. Biol. Trace Elem. Res., 133: 203–211. https://doi.org/10.1007/s12011-009-8431-9

Franklin SB, Young MB, Ciacciariello M (2022). The impact of different sources of zinc, manganese, and copper on broiler performance and excreta output. Animals, 12(9): 1067. https://doi.org/10.3390/ani12091067

Gilbert R, Peto T, Lengyel I, Emri E (2019). Zinc nutrition and inflammation in the aging retina. Mol. Nutr. Food Res., 63(15): 1801049. https://doi.org/10.1002/mnfr.201801049

Hafez A, Nassef E, Fahmy M, Elsabagh M, Bakr A, Hegazi E (2020). Impact of dietary nano-zinc oxide on immune response and antioxidant defense of broiler chickens. Environ. Sci. Pollut. Res., 27(16): 19108–19114. https://doi.org/10.1007/s11356-019-04344-6

Hambidge KM (2010). Micronutrient bioavailability: Dietary reference intakes and a future perspective. Am. J. Clin. Nutr., 91(5): 1430S-1432S. https://doi.org/10.3945/ajcn.2010.28674B

Hatab MH, Badran AMM, Elaroussi MA, Rashad E, Taleb AMA, Elokil AA (2023). Effect of Zinc Oxide Nanoparticles as Feed Additive on Blood Indices, Physiological, Immunological Responses, and Histological Changes in Broiler Chicks. Biol. Trace Elem. Res., pp. 1–15. https://doi.org/10.1007/s12011-023-03820-y

Hatab MH, Rashad E, Saleh HM, El-Sayed E-SR (2022). Effects of dietary supplementation of zinc oxide nanoparticles on productive performance, physiological, histological changes and tissues zn concentration in broiler chicks. Sci. Rep., 12: 18791. https://doi.org/10.1038/s41598-022-22836-3

Hennig B, Wang Y, Ramasamy S, McClain CJ (1993). Zinc protects against tumor necrosis factor-induced disruption of porcine endothelial cell monolayer integrity. J. Nutr., 123(6): 1003–1009. https://doi.org/10.1093/jn/123.6.1003

Hu P, Li K, Peng X, Yao T, Zhu C, Gu H, Liu HY, Sun M, Hu Y, Ennab W (2024). Zinc intake ameliorates intestinal morphology and oxidative stress of broiler chickens under heat stress. Front. Immunol., 14: 1308907. https://doi.org/10.3389/fimmu.2023.1308907

Hu X, Sheikhahmadi A, Li X, Wang Y, Jiao H, Lin H, Zhang B, Song Z (2016). Effect of zinc on appetite regulatory peptides in the hypothalamus of Salmonella-challenged broiler chickens. Biol. Trace Elem. Res., 172(1): 228–233. https://doi.org/10.1007/s12011-015-0582-2

Hu Y, Song W, Zhang W, Du X, Lin X, Liu H-C, Odle J, See MT, Cui X, Li T (2025). Dietary Zn proteinate alleviates heat stress-induced intestinal integrity disruption possibly by promoting cell proliferation via related signaling pathways in the jejunum of broilers. J. Integr. Agric., https://doi.org/10.1016/j.jia.2025.05.012

Hunde A, Patterson P, Ricke S, Kim WK (2012). Supplementation of poultry feeds with dietary zinc and other minerals and compounds to mitigate nitrogen emissions: A review. Biol. Trace Elem. Res., 147: 386–394. https://doi.org/10.1007/s12011-011-9310-8

Hussan F, Krishna D, Preetam VC, Reddy PB, Gurram S (2022). Dietary supplementation of nano zinc oxide on performance, carcass, serum and meat quality parameters of commercial broilers. Biol. Trace Elem. Res., 200(1): 348–353. https://doi.org/10.1007/s12011-021-02635-z

Ibrahim D, Ali H, El-Mandrawy S (2017). Effects of different zinc sources on performance, bio distribution of minerals and expression of genes related to metabolism of broiler chickens. Zagazig Vet. J., 45(3): 292–304. https://doi.org/10.21608/zvjz.2017.7954

Idowu O, Ajuwon O, Oso A (2011). Effects of zinc supplementation on laying performance, serum chemistry and zn residue in tibia bone, liver. Int. J. Poult. Sci., 10(3): 225–230. https://doi.org/10.3923/ijps.2011.225.230

Jahanian R, Yaghoubi MJ (2010). Dietary zinc source and level affect cellular and humoral immune functions in broiler chickens. In: 2nd International Veterinary Poultry Congress, Tehran, Iran. p. 201.

Jain AK, Mishra A, Singh AP, Patel P, Sheikh AA, Chandraker TR, Vandre R (2021). Effects of different concentration of organic and inorganic trace minerals (zinc, selenium, and chromium) supplementation on expression of chTLR4 gene and humoral immune response in broilers. Vet. World, 14(5): 1093. https://doi.org/10.14202/vetworld.2021.1093-1101

Jankowski J, Ognik K, Kozłowski K, Stępniowska A, Zduńczyk Z (2019). Effect of different levels and sources of dietary copper, zinc and manganese on the performance and immune and redox status of turkeys. Animals, 9(11): 883. https://doi.org/10.3390/ani9110883

Jiang J, Pi J, Cai J (2018). The advancing of zinc oxide nanoparticles for biomedical applications. Bioinorg. Chem. Appl., 2018(1): 1062562. https://doi.org/10.1155/2018/1062562

Kandeel M, Akhtar T, Zaheer T, Ahmad S, Ashraf U, Omar M (2022). Anti-parasitic applications of nanoparticles: A review. Pak. Vet. J., 42(2).

Khan RU, Shabana Naz SN, Kuldeep Dhama KD (2014). Chromium: Pharmacological applications in heat-stressed poultry. Int. J. Pharm., 10(4): 213–217. https://doi.org/10.1016/j.chroma.2014.03.080

King JC (2011). Zinc: An essential but elusive nutrient. Am. J. Clin. Nutr., 94(2): 679S-684S. https://doi.org/10.3945/ajcn.110.005744

Kogut MH, Genovese KJ, Swaggerty CL, He H, Broom L (2018). Inflammatory phenotypes in the intestine of poultry: Not all inflammation is created equal. Poult. Sci., 97(7): 2339–2346. https://doi.org/10.3382/ps/pey087

Kwiecień M, Winiarska-Mieczan A, Milczarek A, Tomaszewska E, Matras J (2016). Effects of zinc glycine chelate on growth performance, carcass characteristics, bone quality, and mineral content in bone of broiler chicken. Livest. Sci., 191: 43–50. https://doi.org/10.1016/j.livsci.2016.07.005

Lail N, Sattar A, Omer MO, Hafeez MA, Khalid AR, Mahmood S, Shabbir MA, Ahmed W, Aleem MT, Alouffi A (2023). Biosynthesis and characterization of zinc oxide nanoparticles using Nigella sativa against coccidiosis in commercial poultry. Sci. Rep., 13(1): 6568. https://doi.org/10.1038/s41598-023-33416-4

Lee SR (2018). Critical role of zinc as either an antioxidant or a prooxidant in cellular systems. Oxid. Med. Cell. Longev., 2018(1): 9156285. https://doi.org/10.1155/2018/9156285

Leeson S, Summers JD (2009). Commercial poultry nutrition. Nottingham University Press. https://doi.org/10.7313/UPO9781904761099

Li C, Guo S, Gao J, Guo Y, Du E, Lv Z, Zhang B (2015). Maternal high-zinc diet attenuates intestinal inflammation by reducing DNA methylation and elevating H3K9 acetylation in the A20 promoter of offspring chicks. J. Nutr. Biochem., 26(2): 173–183. https://doi.org/10.1016/j.jnutbio.2014.10.005

Liao X, Li A, Lu L, Liu S, Li S, Zhang L, Wang G, Luo X (2013). Optimal dietary zinc levels of broiler chicks fed a corn–soybean meal diet from 22 to 42 days of age. Anim. Prod. Sci., 53(5): 388–394. https://doi.org/10.1071/AN12291

Liu SB, Li SF, Lu L, Xie JJ, Zhang LY, Wang RL, Luo XG (2013). The effectiveness of zinc proteinate for chicks fed a conventional corn-soybean meal diet. J. Appl. Poult. Res., 22(3): 396–403. https://doi.org/10.3382/japr.2012-00564

Liu ZH, Lu L, Li SF, Zhang LY, Xi L, Zhang KY, Luo XG (2011). Effects of supplemental zinc source and level on growth performance, carcass traits, and meat quality of broilers. Poult. Sci., 90(8): 1782–1790. https://doi.org/10.3382/ps.2010-01215

Lonnerdal B (2000). Dietary factors influencing zinc absorption. J. Nutr., 130(5): 1378S-1383S. https://doi.org/10.1093/jn/130.5.1378S

Ma W, Ali BH (2025). Enhancing of immune response against newcastle disease virus for broiler feeds on zinc-methionine. Iraqi J. Agric. Sci., 56(Special): 123–131. https://doi.org/10.36103/m1rgrx05

Maggini S, Maldonado P, Cardim P, Fernandez Newball C, Sota Latino E (2017). Vitamins C, D and zinc: synergistic roles in immune function and infections. Vitam Min., 6(167): 1318–2376. https://doi.org/10.4172/2376-1318.1000167

Mao SY, Lien TF (2017). Effects of nanosized zinc oxide and γ-polyglutamic acid on eggshell quality and serum parameters of aged laying hens. Arch. Anim. Nutr., 71(5): 373–383. https://doi.org/10.1080/1745039X.2017.1355600

Maret W (2019). The redox biology of redox-inert zinc ions. Free Radic. Biol. Med., 134: 311–326. https://doi.org/10.1016/j.freeradbiomed.2019.01.006

Maret W, Krężel A (2007). Cellular zinc and redox buffering capacity of metallothionein/thionein in health and disease. Mol. Med., 13(7–8): 371–375. https://doi.org/10.2119/2007-00036.Maret

Marreiro D do N, Cruz KJC, Morais JBS, Beserra JB, Severo JS, De Oliveira ARS (2017). Zinc and oxidative stress: current mechanisms. Antioxidants, 6(2): 24. https://doi.org/10.3390/antiox6020024

Mohammadi F, Ahmadi F, Andi MA (2015). Effect of zinc oxide nanoparticles on carcass parameters, relative weight of digestive and lymphoid organs of broiler fed wet diet during the starter period. Int. J. Biosci., 6(2): 389–394. https://doi.org/10.12692/ijb/6.2.389-394

Mohammadi V, Ghazanfari S, Mohammadi-Sangcheshmeh A, Nazaran MH (2015). Comparative effects of zinc-nano complexes, zinc-sulphate and zinc-methionine on performance in broiler chickens. Br. Poult. Sci., 56(4): 486–493. https://doi.org/10.1080/00071668.2015.1064093

Mohd Yusof H, Abdul Rahman N, Mohamad R, Zaidan UH, Samsudin AA (2022). Influence of dietary biosynthesized zinc oxide nanoparticles on broiler zinc uptake, bone quality, and antioxidative status. Animals, 13(1): 115. https://doi.org/10.3390/ani13010115

Mohd Yusof H, Mohamad R, Zaidan UH, Abdul Rahman N (2019). Microbial synthesis of zinc oxide nanoparticles and their potential application as an antimicrobial agent and a feed supplement in animal industry: A review. J. Anim. Sci. Biotechnol., 10: 1–22. https://doi.org/10.1186/s40104-019-0368-z

Mozhiarasi V, Karunakaran R, Raja P, Radhakrishnan L (2023). Effects of zinc oxide nanoparticles supplementation on growth performance, meat quality and serum biochemical parameters in broiler chicks. Biol. Trace Elem. Res., pp. 1–16. https://doi.org/10.1007/s12011-023-03759-0

Naz S, Idris M, Khalique MA, Zia-Ur-Rahman, Alhidary IA, Abdelrahman MM, Khan RU, Chand N, Farooq U, Ahmad S (2016). The activity and use of zinc in poultry diets. Worlds. Poult. Sci. J., 72(1): 159–167. https://doi.org/10.1017/S0043933915002755

NRC (National Research Council) (1994). Nutrient requirements of poultry ed. National Academy of Sciences NRC, Washington, DC.

Olechnowicz J, Tinkov A, Skalny A, Suliburska J (2018). Zinc status is associated with inflammation, oxidative stress, lipid, and glucose metabolism. J. Physiol. Sci., 68(1): 19–31. https://doi.org/10.1007/s12576-017-0571-7

Olukosi OA, van Kuijk S, Han Y (2018). Copper and zinc sources and levels of zinc inclusion influence growth performance, tissue trace mineral content, and carcass yield of broiler chickens. Poult. Sci., 97(11): 3891–3898. https://doi.org/10.3382/ps/pey247

Özcelik D, Nazıroglu M, Tunçdemir M, Çelik Ö, Öztürk M, Flores-Arce MF (2012). Zinc supplementation attenuates metallothionein and oxidative stress changes in kidney of streptozotocin-induced diabetic rats. Biol. Trace Elem. Res., 150(1): 342–349. https://doi.org/10.1007/s12011-012-9508-4

Pang Y, Applegate TJ (2007). Effects of dietary copper supplementation and copper source on digesta pH, calcium, zinc, and copper complex size in the gastrointestinal tract of the broiler chicken. Poult. Sci., 86(3): 531–537. https://doi.org/10.1093/ps/86.3.531

Patra A, Lalhriatpuii M (2020). progress and prospect of essential mineral nanoparticles in poultry nutrition and feeding: A review. Biol. Trace Elem. Res., 197(1): 233–253. https://doi.org/10.1007/s12011-019-01959-1

Pereira CG, Rabello CB-V, Barros MR, Manso HECCC, Santos MJB dos, Faria AG, Oliveira HB de, Medeiros-Ventura WRL, Silva Junior RV, Carvalho CCD (2020). Zinc, manganese and copper amino acid complexed in laying hens’ diets affect performance, blood parameters and reproductive organs development. PLoS One, 15(11): e0239229. https://doi.org/10.1371/journal.pone.0239229

Pimentel JL, Cook ME, Greger JL (1991). Immune response of chicks fed various levels of zinc. Poult. Sci., 70(4): 947–954. https://doi.org/10.3382/ps.0700947

Prabakar G, Gopi M, Kolluri G, Rokade JJ, Khillare G, Pearlin B V, Jadhav SE, Tyagi JS, Mohan J (2021). Effect of supplementation of zinc-methionine on egg production, semen quality, reproductive hormones, and hatchability in broiler breeders. Biol. Trace Elem. Res., 199(12): 4721–4730. https://doi.org/10.1007/s12011-021-02590-9

Prasad AS (1991). Discovery of human zinc deficiency and studies in an experimental human model. Am. J. Clin. Nutr., 53(2): 403–412. https://doi.org/10.1093/ajcn/53.2.403

Qu J, Zuo X, Xu Q, Li M, Zou L, Tao R, Liu X, Wang X, Wang J, Wen L (2023). Effect of two particle sizes of nano zinc oxide on growth performance, immune function, digestive tract morphology, and intestinal microbiota composition in broilers. Animals, 13(9): 1454. https://doi.org/10.3390/ani13091454

Quarterman J (1968). The metabolic role of zinc with special reference to carbohydrate and lipid metabolism. Rowett Ros. Inst. Rep., 24: 100.

Quarterman J, Humphries WR, Florence E (1969). Changes in appetite and alimentary muco-substances in zinc deficiency. In: Proc. Int. Symp. Trace Element. Metab. Anim.,

Rahman MM, Wahed MA, Fuchs GJ, Baqui AH, Alvarez JO (2002). Synergistic effect of zinc and vitamin A on the biochemical indexes of vitamin A nutrition in children. Am. J. Clin. Nutr., 75(1): 92–98. https://doi.org/10.1093/ajcn/75.1.92

Ramiah SK, Atta Awad E, Hemly NIM, Ebrahimi M, Joshua O, Jamshed M, Saminathan M, Soleimani AF, Idrus Z (2020). Effects of zinc oxide nanoparticles on regulatory appetite and heat stress protein genes in broiler chickens subjected to heat stress. J. Anim. Sci., 98(10): skaa300. https://doi.org/10.1093/jas/skaa300

Ramiah SK, Awad EA, Mookiah S, Idrus Z (2019). Effects of zinc oxide nanoparticles on growth performance and concentrations of malondialdehyde, zinc in tissues, and corticosterone in broiler chickens under heat stress conditions. Poult. Sci., 98(9): 3828–3838. https://doi.org/10.3382/ps/pez093

Ren Y, Sun Y, Javad HU, Wang R, Zhou Z, Huang Y, Shu X, Li C (2025). Growth performance of and liver function in heat-stressed magang geese fed the antioxidant zinc ascorbate and its potential mechanism of action. Biol. Trace Elem. Res., 203(2): 1035–1047. https://doi.org/10.1007/s12011-024-04220-6

Rezapour A, Gharahveysi S, Khorshidi KJ, Abdolahpour R (2024). Effects of organic mineral chelates of zinc, manganese, and chromium on growth performance, physiological, hematological, intestinal microflora, immunological, and bone traits in broiler chickens. Braz. J. Poult. Sci., 26(04): eRBCA-2024. https://doi.org/10.1590/1806-9061-2024-1992

Rossi P, Rutz F, Anciuti MA, Rech JL, Zauk NHF (2007). Influence of graded levels of organic zinc on growth performance and carcass traits of broilers. J. Appl. Poult. Res., 16(2): 219–225. https://doi.org/10.1093/japr/16.2.219

Rouhalamini SM, Salarmoini M, Asadi-Karam G (2014). Effect of zinc sulfate and organic chromium supplementation on the performance, meat quality and immune response of Japanese quails under heat stress conditions. Poult. Sci. J., 2(2): 165–181.

Saenmahayak B, Bilgili SF, Hess JB, Singh M (2010). Live and processing performance of broiler chickens fed diets supplemented with complexed zinc. J. Appl. Poult. Res., 19(4): 334–340. https://doi.org/10.3382/japr.2010-00166

Saenmahayak B, Singh M, Bilgili SF, Hess JB (2012). Influence of dietary supplementation with complexed zinc on meat quality and shelf life of broilers. Int. J. Poult. Sci., 11(1), 28-32. https://doi.org/10.3923/ijps.2012.28.32

Sahin K, Sahin N, Kucuk O, Hayirli A, Prasad AS (2009). Role of dietary zinc in heat-stressed poultry: A review. Poult. Sci., 88(10): 2176–2183. https://doi.org/10.3382/ps.2008-00560

Sahin K, Smith MO, Onderci M, Sahin N, Gursu MF, Kucuk O (2005). Supplementation of zinc from organic or inorganic source improves performance and antioxidant status of heat-distressed quail. Poult. Sci., 84(6): 882–887. https://doi.org/10.1093/ps/84.6.882

Sahoo A, Swain RK, Mishra SK (2014). Effect of inorganic, organic and nano zinc supplemented diets on bioavailability and immunity status of broilers. Int. J. Adv. Res., 2(11): 828–837.

Sahraei M, Janmmohamadi H, Taghizadeh A, Moghadam AG, Rafat SA (2012). Estimation of the relative bioavailability of several zinc sources for broilers when fed a conventional diet. Biotechnol. Anim. Husb., 28(3): 441–453. https://doi.org/10.2298/BAH1203441S

Sahraei M, Janmmohamadi H, Taghizadeh A, Moghadam GA, Rafat SA (2013). Estimation of the relative bioavailability of several zinc sources for broilers fed a conventional corn-soybean meal diet. J. Poult. Sci., 50(1): 53–59. https://doi.org/10.2141/jpsa.0120022

Sajadifar S, Miranzadeh H, Moazeni M (2011). Immune responses of broiler chicks supplemented with high levels of zinc. Online J. Anim. Feed Res., 6(2): 493–496.

Sajadifar S, Miranzadeh H, Moazeni M (2013). Effect of zinc on humoral and cell-mediated immunity of broilers vaccinated against coccidiosis. Iran. J. Parasitol., 8(3): 474.

Salabi F, Boujarpoor M, Fayazi J, Salari S, Nazari M (2011). Effects of different levels of zinc on the performance and carcass characteristics of broiler rearedunder heat stress condition. J. Anim. Vet. Adv., 10(10): 1332–1335. https://doi.org/10.3923/javaa.2011.1332.1335

Salama AAK, Caja G, Albanell E, Such X, Casals R, Plaixats J (2003). Effects of dietary supplements of zinc-methionine on milk production, udder health and zinc metabolism in dairy goats. J. Dairy Res., 70(1): 9–17. https://doi.org/10.1017/S0022029902005708

Saleh AA, Eid YZ, Ebeid TA, Ohtsuka A, Yamamoto M, Hayashi K (2012). Feeding Aspergillus awamori reduces skeletal muscle protein breakdown and stimulates growth in broilers. Anim. Sci. J., 83(8): 594–598. https://doi.org/10.1111/j.1740-0929.2011.00999.x

Saleh AA, Ragab MM, Ahmed EAM, Abudabos AM, Ebeid TA (2018). Effect of dietary zinc-methionine supplementation on growth performance, nutrient utilization, antioxidative properties and immune response in broiler chickens under high ambient temperature. J. Appl. Anim. Res., 46(1): 820–827. https://doi.org/10.1080/09712119.2017.1407768

Salim HM, Jo C, Lee BD (2008). Zinc in broiler feeding and nutrition. Avian Biol. Res., 1(1): 5–18. https://doi.org/10.3184/175815508X334578

Salim HM, Lee HR, Jo C, Lee SK, Lee BD (2012). Effect of dietary zinc proteinate supplementation on growth performance, and skin and meat quality of male and female broiler chicks. Br. Poult. Sci., 53(1): 116–124. https://doi.org/10.1080/00071668.2012.658757

Salim HM, Lee H-R, Jo C-R, Lee S-K, Lee B-D (2011). Influence of various levels of organic zinc on the live performance, meat quality attributes, and sensory properties of broiler chickens. Food Sci. Anim. Resour., 31(2): 207–214. https://doi.org/10.5851/kosfa.2011.31.2.207

Sanna A, Firinu D, Zavattari P, Valera P (2018). Zinc status and autoimmunity: a systematic review and meta-analysis. Nutrients, 10(1), 68.

Santos TS dos, Augusto KVZ, Han Y, Sartori MMP, Denadai JC, Santos CT, Sobral NC, Roça RO, Sartori JR (2021). High levels of copper and zinc supplementation in broiler diets on growth performance, carcase traits and apparent ileal mineral absorption. Br. Poult. Sci., 62(4): 579–588. https://doi.org/10.1080/00071668.2021.1887453

Sarvari BG, Seyedi AH, Shahryar HA, Sarikhan M, Ghavidel SZ (2015). Effects of dietary zinc oxide and a blend of organic acids on broiler live performance, carcass traits, and serum parameters. Braz. J. Poult. Sci., 17: 39–45. https://doi.org/10.1590/1516-635XSPECIALISSUENutrition-PoultryFeedingAdditives039-046

Selim NA, Amira M, Khosht AR, Abd El-Hakim AS (2014). Effect of sources and inclusion levels of zinc in broiler diets containing different vegetable oils during summer season conditions on meat quality. Int. J. Poult. Sci., 13(11): 619. https://doi.org/10.3923/ijps.2014.619.626

Sevim Ö, Ahsan U, Tatlı O, Kuter E, Khamseh EK, Temiz AR, Özdemir ÖS, Aydın AK, Özsoy B, Köksal BH (2021). Effect of high stocking density and dietary nano-zinc on growth performance, carcass yield, meat quality, feathering score, and footpad dermatitis in broiler chickens. Livest. Sci., 253: 104727. https://doi.org/10.1016/j.livsci.2021.104727

Shah M, Zaneb H, Masood S, Khan I, Sikandar A, Ashraf S, Rehman HF, Usman MM, Khan FA, Amanullah H (2018). Effect of zinc and probiotics supplementation on performance and immune organs morphology in heat stressed broilers. S. Afr. J. Anim. Sci., 48(6). https://doi.org/10.4314/sajas.v48i6.3

Sherif R, Nassef E, El-Kassas S, Bakr A, Hegazi E, El-Sawy H (2024). Synergistic impact of Chlorella vulgaris, zinc oxide-and/or selenium nanoparticles dietary supplementation on broiler’s growth performance, antioxidant and blood biochemistry. Trop. Anim. Health Prod., 56(7): 246. https://doi.org/10.1007/s11250-024-04098-5

Shi B, Jin M, Jiao L, Betancor MB, Tocher DR, Zhou Q (2020). Effects of dietary zinc level on growth performance, lipolysis and expression of genes involved in the calcium/calmodulin-dependent protein kinase kinase-β/AMP-activated protein kinase pathway in juvenile Pacific white shrimp. Br. J. Nutr., 124(8): 773–784. https://doi.org/10.1017/S0007114520001725

Sobhi BM, Ismael EY, Elleithy E, Elsabagh M, Fahmy KNE (2020). Influence of combined yeast-derived zinc, selenium and chromium on performance, carcass traits, immune response and histomorphological changes in broiler chickens. J. Adv. Vet. Res., 10(4): 233–240.

Song Z, Lv J, Sheikhahmadi A, Uerlings J, Everaert N (2017). Attenuating effect of zinc and vitamin E on the intestinal oxidative stress induced by silver nanoparticles in broiler chickens. Biol. Trace Elem. Res., 180(2): 306–313. https://doi.org/10.1007/s12011-017-1016-0

Soni N, Mishra SK, Swain R, Das A, Chichilichi B, Sethy K (2013). Bioavailability and immunity response in broiler breeders on organically complexed zinc supplementation. Food Nutr. Sci., 4(12): 1293. https://doi.org/10.4236/fns.2013.412166

Spencer H, Kramer L, Norris C, Osis D (1984). Effect of calcium and phosphorus on zinc metabolism in man. Am. J. Clin. Nutr., 40(6): 1213–1218. https://doi.org/10.1093/ajcn/40.6.1213

Star L, Van der Klis JD, Rapp C, Ward TL (2012). Bioavailability of organic and inorganic zinc sources in male broilers. Poult. Sci., 91(12): 3115–3120. https://doi.org/10.3382/ps.2012-02314

Stiles LI, Ferrao K, Mehta KJ (2024). Role of zinc in health and disease. Clin. Exp. Med., 24(1): 38. https://doi.org/10.1007/s10238-024-01302-6

Sukhanova A, Bozrova S, Sokolov P, Berestovoy M, Karaulov A, Nabiev I (2018). Dependence of nanoparticle toxicity on their physical and chemical properties. Nanoscale Res. Lett., 13: 1–21. https://doi.org/10.1186/s11671-018-2457-x

Sunder GS, Kumar CV, Panda AK, Raju M, Rao SVR (2013). Effect of supplemental organic Zn and Mn on broiler performance, bone measures, tissue mineral uptake and immune response at 35 days of age. Curr. Res. Poult. Sci., 3(1): 1–11. https://doi.org/10.3923/crpsaj.2013.1.11

Suttle NF (2022). Mineral nutrition of livestock. Oxfordshire, UK: CAB International. https://doi.org/10.1079/9781789240924.0000

Tabatabaie MM, Aliarabi H, Saki AA, Ahmadi A, Siyar SA (2007). Effect of different sources and levels of zinc on egg quality and laying hen performance. Pak. J. Biol. Sci., 10(19): 3476–3478. https://doi.org/10.3923/pjbs.2007.3476.3478

Vieira MM, Ribeiro AML, Kessler AM, Moraes ML, Kunrath MA, Ledur VS (2013). Different sources of dietary zinc for broilers submitted to immunological, nutritional, and environmental challenge. J. Appl. Poult. Res., 22(4): 855–861. https://doi.org/10.3382/japr.2013-00753

Virden WS, Yeatman JB, Barber SJ, Zumwalt CD, Ward TL, Johnson AB, Kidd MT (2003). Hen mineral nutrition impacts progeny livability. J. Appl. Poult. Res., 12(4): 411–416. https://doi.org/10.1093/japr/12.4.411

Waeothong T, Lee JW, Hsia LC (2021). Investigation of the zinc accumulation in the tissue and performance in broilers raisedwith high levels of zinc sulfate feed under heat stress. Turk. J. Vet. Anim. Sci., 45(3): 427–436. https://doi.org/10.3906/vet-1911-65

Wedekind KJ, Hortin Ae, Baker DH (1992). Methodology for assessing zinc bioavailability: efficacy estimates for zinc-methionine, zinc sulfate, and zinc oxide. J. Anim. Sci., 70(1): 178–187. https://doi.org/10.2527/1992.701178x

Welch RM, Graham RD (2012). Perspectives on enhancing the nutritional quality of food crops with trace elements. Fertil. Crop. Improv. Hum. Health Sci. Rev., 65.

Wen M, Zhao H, Liu G, Chen X, Wu B, Tian G, Cai J, Jia G (2018). Effect of zinc supplementation on growth performance, intestinal development, and intestinal barrier-related gene expression in Pekin ducks. Biol. Trace Elem. Res., 183(2): 351–360. https://doi.org/10.1007/s12011-017-1143-7

Wijnhoven SWP, Peijnenburg WJGM, Herberts CA, Hagens WI, Oomen AG, Heugens EHW, Roszek B, Bisschops J, Gosens I, Van De Meent D (2009). Nano-silver: A review of available data and knowledge gaps in human and environmental risk assessment. Nanotoxicology, 3(2): 109–138. https://doi.org/10.1080/17435390902725914

Yogesh K, Deo C, Shrivastava HP, Mandal AB, Wadhwa A, Singh I (2013). Growth performance, carcass yield, and immune competence of broiler chickens as influenced by dietary supplemental zinc sources and levels. Agric. Res., 2: 270–274. https://doi.org/10.1007/s40003-013-0067-5

Yusof HM, Rahman NA, Mohamad R, Zaidan UH, Arshad MA, Samsudin AA (2023). Effects of dietary zinc oxide nanoparticles supplementation on broiler growth performance, zinc retention, liver health status, and gastrointestinal microbial load. J. Trace Elem. Miner., 4: 100072. https://doi.org/10.1016/j.jtemin.2023.100072

Zaghari M, Avazkhanllo M, Ganjkhanlou M (2018). Reevaluation of male broiler zinc requirement by dose-response trial using practical diet with added exogenous phytase. J. Agr. Sci. Tech., 17: 333-343.

Zaghari M, Mehrvarz H, Hajati H, Moravej H (2022). Evaluation of an innovative Zn source on feed efficiency, growth performance, skin and bone quality of broilers suffering heat stress. Animals, 12(23): 3272. https://doi.org/10.3390/ani12233272

Zhang TY, Liu JL, Zhang JL, Zhang N, Yang X, Qu HX, Xi L, Han JC (2018). Effects of dietary zinc levels on the growth performance, organ zinc content, and zinc retention in broiler chickens. Rev. Bras. Ciência Avícola, 20(01): 127–132. https://doi.org/10.1590/1806-9061-2017-0604

Zhao CY, Tan SX, Xiao XY, Qiu XS, Pan JQ, Tang ZX (2014). Effects of dietary zinc oxide nanoparticles on growth performance and antioxidative status in broilers. Biol. Trace Elem. Res., 160(3): 361–367. https://doi.org/10.1007/s12011-014-0052-2

Zhu YW, Li WX, Lu L, Zhang LY, Ji C, Lin X, Liu HC, Odle J, Luo XG (2017). Impact of maternal heat stress in conjunction with dietary zinc supplementation on hatchability, embryonic development, and growth performance in offspring broilers. Poult. Sci., 96(7): 2351–2359. https://doi.org/10.3382/ps/pew481