AAVS_14_9_1878-1891

INTRODUCTION

Management of dairy calves from birth to the weaning period is a critical component of dairy farming. This stage requires special attention to ensure that calves grow optimally, particularly through the appropriate feed intake management (Tanuwiria et al., 2020). Calves demonstrating strong early performance are more likely to become high-quality replacement or breeding stock (Wang et al., 2020; Palczynski et al., 2022). Adequate nutrition and effective feed management are fundamental to supporting optimal growth and development (Syahrial et al., 2022). Ockenden et al. (2025) emphasize that providing adequate nutrition during the early life stages of calves has long-term impacts on livestock performance, including growth rate, milk yield, and production efficiency.

Providing nutritionally balanced diets tailored to the physiological requirements of calves is critical for supporting metabolic function and overall health. Because calves have an underdeveloped rumen, their capacity to efficiently digest high-fiber feed is limited. Consequently, calf diets should be formulated with a relatively high crude protein (CP) content, ranging from 16–22% depending on the developmental phase, and a fat content of 15–20%. In addition, adequate mineral supplementation particularly calcium (0.70–1.00%), phosphorus (0.40–1.00%), magnesium (0.10–0.20%), potassium (0.65–1.00%), and sodium (0.15%) is essential to support optimal skeletal growth and bone development (NASEM, 2021). Diets high in crude fiber should be avoided during this stage, as excessive fiber levels and long particle sizes can reduce starter feed intake and impair rumen development, ultimately compromising growth performance (Xiao et al., 2024). Newborn calves possess an immature immune system that remains underdeveloped until weaning (Sahara et al., 2025). The weaning period represents a critical transition from liquid to solid feed, prompting substantial changes in the digestive and metabolic systems (Mirzaei et al., 2020). Challenges in adapting to solid feed, particularly those containing fiber, frequently lead to disorders such as diarrhea, malnutrition, and infection, thereby increasing mortality risk (Quigley, 2024). Beyond the risk of suboptimal growth, calves are highly susceptible to infectious diseases and metabolic disorders that may lead to mortality (Symonds et al., 2016). Nutrient deficiencies during the early growth stages of calves can result in severe health disorders and impaired growth performance. Such nutritional inadequacies have long-term consequences, including reduced productivity and compromised reproductive efficiency later in life (Fischer et al., 2020; Fentie et al., 2020). Proper feeding management is reflected in the metabolic status and overall health of the calf. Nutrient deficiencies can trigger a range of metabolic disturbances, physiological stress, stunted growth, anemia, diarrhea, malnutrition, musculoskeletal disorders, acidosis and even death (Ahmad et al., 2025).

Ayunita et al. (2022) further emphasizes that prolonged nutrient deficiencies can impair metabolic processes and reduce calf productivity. One of the key strategies to improve nutritional quality is through the provision of high-quality feed, the inclusion of feed supplements and feed additives, and the development of feed-engineering innovations designed to optimize nutrient utilization in calves. This review comprehensively examines the nutritional status and rumen development of dairy calves across different weaning stages, with a particular emphasis on nutritional strategies aimed at optimizing growth performance and supporting proper rumen maturation. The life stages of calves are generally classified into three phases: The pre-weaning, the weaning, and the post-weaning phase.

Pre-weaning period: Nutritional and metabolic considerations

The pre-weaning phase is the initial stage of a calf’s life, beginning at birth and continuing until the onset of weaning, during which the calf still obtains most of its nutritional requirements from maternal milk or milk replacer (Ockenden et al., 2025). This period generally lasts until the calf reaches approximately 6–8 weeks of age, depending on the management system applied. During this stage, the primary focus includes the immediate provision of colostrum after birth to supply essential antibodies, the administration of milk or milk replacer as the main sources of energy and protein, the introduction of solid feed (starter) to stimulate rumen development, and comprehensive health management to prevent diarrhea and respiratory disease.

Newborn calves are highly susceptible to infectious diseases due to their immature immune system. During the first 24–48 hours of life, prior to colostrum intake, dairy calves exhibit low circulating antibody levels, with blood immunoglobulin G (IgG) concentrations of approximately 11–13 g/L (Goetz et al., 2025; Salimah et al., 2022). Following adequate colostrum consumption, serum IgG concentrations increase substantially, reaching approximately 20–26 g/L, thereby providing passive immunity essential for early-life health and survival (Salimah et al., 2022), to survive exposure to pathogenic microbes. IgG are the most critical factor influencing early immune protection in calves. Consequently, colostrum is regarded as the most essential feed for pre-weaning calves aged 0–1 week. Colostrum contains high levels of IgG, reaching up to 60-90 g/L (Stockler and Chomorro, 2021; Roder et al. 2023). Early colostrum intake also supports the development of the gastrointestinal tract (Westhoff et al., 2024). In addition to conferring passive immunity, early colostrum intake plays a crucial role in supporting gastrointestinal tract development in newborn calves (Westhoff et al., 2024). Consequently, timely colostrum feeding is essential not only for immunological protection but also for fulfilling the calf’s immediate nutritional requirements, including high-quality proteins, carbohydrates, lipids, vitamins, and minerals. These nutrients are fundamental for maintaining metabolic homeostasis, supporting normal postnatal growth, and facilitating effective antibody synthesis during the early stages of life (Silva et al., 2024).

Calves typically begin ruminating at approximately 2–3 weeks of age. Rumination, a physiological process that distinguishes ruminants from monogastric animals, plays a crucial role in enhancing the mechanical breakdown and microbial digestion of plant-based feeds, thereby stimulating overall digestive efficiency. The proportion of time devoted to rumination progressively increases throughout the pre-weaning period as the rumen develops. During this stage, calves typically ruminate for approximately 0–80 minutes per day and spend about 4–8 hours per day standing, reflecting ongoing behavioral and physiological adaptation

Table 1: Comparison of Milk Feeding Strategies for Pre-Weaning Calves.

Referens	Treatment	Result
Alimirzaei et al., 2020.	Comparing two methods for dairy calves during the pre-weaning period, namely conventional feeding (CF) which is generally given and intensified feeding (IF) Intensified milk-fed calves received 0.91, 0.98, and 1.02 kg of DM per day for the first, second, and third weeks, respectively. In CF, calves are fed milk amounting to 10% of their body weight per day conventionally, while in IF calves are fed intensively with milk amounting to 20% of their body weight during the first three weeks, then gradually reduced to 10% of their body weight.	The results show that calves fed milk using the IF method are more tolerant to disease, have higher immunity, and have lower stress and inflammation levels at the outset.
Ockenden et al., 2023	Comparing the effects of feeding 4 liters of milk versus 8 liters per day to pre-weaning dairy calves. This study used 20 female Friesian Holstein dairy calves in each treatment.	It was found that calves fed 8 liters of milk showed significantly higher body weight starting at 2 weeks of age. In addition, these calves had a body weight 19 kg higher at weaning, as well as better immune and metabolic responses.
Mirzaei et al., 2018	Calves were divided into one of four treatments. (1) calves fed a moderate level of milk (MPM) and weaned at 60 days of age (total milk intake = 317 liters), (2) calves fed MPM and weaned at 75 days of age (total milk intake = 313 liters), (3) calves fed a high level of milk (HPM) and weaned on day 60 (total milk intake = 411 liters); and (4) calves fed HPM and weaned on day 75 of age (total milk intake = 407 liters).	The results show that calves fed high amounts of milk during the pre-weaning period benefited from extending the weaning period from 60 to 75 days of age based on average daily weight gain, feed efficiency, and final body weight
Leal et al., 2025	Testing the effect of milk replacer (MR) administration at two different levels on Holstein dairy calves during the pre-weaning period. The treatments administered were: Elevated Level of Nutrient Intake (ELE) group: given 8 liters of MR per day (5.41 Mcal ME) and Restricted Level of Nutrient Intake (RES) group: given 4 liters of MR per day (2.71 Mcal ME).	High MR administration during the pre-weaning period enhances early growth and has long-term effects on energy metabolism and insulin sensitivity, but does not significantly affect medium-term reproductive performance. In the ELE group, the average daily weight gain resulted in higher body weight at 70 days of age (±9 kg).

associated with rumen maturation (Wang et al., 2022; McPherson et al., 2024). Pre-weaning calves possess an underdeveloped digestive system that still resembles that of monogastric animals, during this phase, dairy calves are generally provided with maternal milk or milk replacer as their primary nutrient source (Morin et al., 2021).

During the first 2–3 weeks of life, dairy calves undergo an exceptionally rapid phase of physical development (Mortazavi et al., 2025). At this stage, they require sufficient nutrient intake, including milk at approximately 8–10% of their body weight, to support optimal growth. Nutritious and well-balanced feed plays a crucial role in promoting the maturation of the digestive tract. In contrast, inadequate nutrient intake can trigger metabolic irregularities (Chapelain et al., 2025), which may subsequently impair growth performance, compromise health status, and disrupt the balance of the gut microbiota. Such deficiencies can also elevate mortality rates in dairy calves to around 7.5–10% within the first two weeks of life (Alimirzaei et al., 2020).

The early postnatal period, particularly between two and three weeks after birth, is considered the most vulnerable phase for calves because their digestive capacity is still limited, even though their nutritional requirements are markedly high. This critical window is characterized by a surge in digestive secretions and enzyme activity (NASEM, 2001). At this point, the abomasum is the only compartment of the stomach that is fully functional, and the digestion of fats, carbohydrates, and proteins relies mainly on enzymes produced in the abomasum and small intestine, similar to the digestive processes observed in monogastric animals (Diao et al., 2019). Due to this physiological immaturity, calves are particularly susceptible to digestive disturbances such as diarrhea, bloat, and other metabolic complications (Carter et al., 2021). Moreover, from birth until weaning, calves experience substantial dietary shifts that coincide with significant changes in physiological and metabolic functions (Meale et al., 2017). Several studies on the comparison of milk feeding strategies for pre-weaning calves are presented in Table 1.

Weaning transition: Strategies for rumen development and energy balance

The weaning period in dairy calves is defined as the gradual transition from milk consumption either maternal milk or milk replacer to solid feed (calf starter) as the primary source of nutrients (Palczynski et al., 2020). Dairy calves are typically weaned between 6−10 weeks of age (Tao et al., 2017; Abuelo et al., 2019; Barry et al., 2020; Palczynski et al., 2020; Machado and Ballou, 2022). Weaning represents one of the most critical transitional stages in a calf’s life, as its success is strongly influenced by the calf’s adaptive capacity and rumen development (Hao et al., 2021). Optimal rumen development is essential to support maximum growth rates. Several factors are considered when initiating weaning, including age, body weight, and calf starter intake. During this period, milk allowance is gradually reduced while the provision of calf starter is increased (Verdon and Tilbrook, 2021). Rumen development is a key determinant in the weaning process because the rumen is the site of microbial fermentation that converts feed substrates into volatile fatty acids (VFA), which are subsequently absorbed in the intestine. VFA comprising acetate (C2), propionate (C3), and butyrate (C4) are the primary products of carbohydrate fermentation by rumen microbiota. They play a crucial role in the energy metabolism of calves, particularly once calf starter intake begins. Their functions include serving as the main energy source, stimulating rumen growth, and supporting overall metabolic function. In ruminants, the rumen has a dominant role in digestion; therefore, calf starter feeding is essential for stimulating rumen development (Lanier et al., 2022; Drackley, 2025; Ramadan et al., 2025).

During the weaning period, calf mortality tends to be high because this stage represents a critical transition from liquid feed to solid feed (Mirzaei et al., 2020). Gradual weaning is therefore recommended to minimize weaning stress. Under a gradual weaning program, the milk allowance is progressively reduced over an extended period, encouraging calves to increase their intake of calf starter and concentrate feeds (Eckert et al., 2015). Enhanced consumption and improved quality of calf starter during this phase contribute significantly to rumen development, enabling higher post-weaning weight gain (Sweeney et al., 2010; Khan et al., 2011). During this period, the introduction of forage may begin but should be carefully regulated, as excessive forage intake can adversely affect rumen development (Kertz, 2023). This is because forage generally contains high levels of structural fiber, which is difficult for the immature rumen to digest and may result in digestive disturbances or ruminal injury. For this reason, providing high-quality calf starter along with forages low in crude fiber is essential to support rumen health, optimize growth, and enhance overall development (Palczynski et al., 2020). One such option is hydroponic fodder, which offers advantages such as low crude fiber content, short cultivation time, year-round availability and relatively high crude protein levels (Mekuriaw, 2023).

Gradual weaning is considered the most effective strategy for dairy calves, both in terms of welfare and performance (Steele et al., 2017). In addition, several studies have identified various strategies to optimize the performance of dairy calves during the weaning phase are presented in Table 2.

Post-weaning growth: Optimizing nutrient utilization and health

The post-weaning period is the stage in which calves have completely ceased consuming milk either maternal milk or milk replacer and begin adapting fully to solid feed. This phase generally spans from approximately 10 weeks to 4 months of age (Lorenz et al., 2011; Drackley, 2024). During this period, appropriate nutritional management is essential to support optimal growth and prevent health disorders. Calf health and welfare in the post-weaning stage are influenced by feeding management, environmental conditions, and stress associated with separation from the dam (Welk et al., 2024). In addition, the calf’s digestive system undergoes rapid development to maximize nutrient utilization from fibrous feeds (Raeth et al., 2016). Feed provided during this stage typically includes calf starter and suitable forage starter, both formulated to match the functional development of the rumen (Drackley, 2024).

Successful calf management during this stage is critical for determining the future productivity of adult cows as replacement stock, with emphasis on health, growth, and reproductive readiness (Leal et al., 2025). Therefore, a thorough understanding of appropriate post-weaning management plays a pivotal role in ensuring production sustainability and the overall success of dairy farming systems (Carulla et al., 2023). Balancing the provision of concentrate and roughage is essential to maximize nutrient intake, support gastrointestinal development, and minimize reductions in growth rate (Khan et al., 2016). During this phase, calves undergo rapid somatic growth, with a targeted average daily gain (ADG) ranging from 0.7 to 2.0 kg/day (Hurst et al., 2021). Adequate growth during the pre- and post-weaning periods is critical to ensure optimal development and future productivity. Accordingly, the target body weight for post-weaning dairy calves is approximately 425 kg upon entry into the heifer phase at around 15 months of age (Duplessis et al., 2015).

The nutritional status of calves during the post-weaning period is crucial for supporting optimal growth and physiological development, particularly of the rumen and reproductive organs. Their dietary requirements include balanced amounts of energy, protein, carbohydrates, vitamins, and minerals to prevent metabolic disturbances that may negatively affect growth and future reproductive performance (NASEM, 2021). A crude protein level

Table 2: Various Weaning Strategies for Dairy Calves.

Referens	Treatment	Result
Eckert et al., 2015	Weaning at different ages (6 vs. 8 weeks) with different pre-weaning feeding regimes in FH dairy calves	Weaning at 8 weeks of age with adequate starter feed and milk results in better ADG and rumen health compared to 6 weeks of age.
Permana et al., 2023	Weaning of FH dairy calves at 70, 80, and 90 days of age by feeding them a Total Mixed Ration (TMR) combination of feed and concentrate with regulated nutrient content and prepared in specific proportions with the aim of improving production performance. The observation period was 60 days.	Weaning at 70 days with TMR provides the best feed intake performance, optimal ADG, final weight of 89.2 kg, and highest feed efficiency.
Mao et al., 2017	Weaning of yellow cattle calves (China) with different weaning times. Calves were divided into three treatments, namely weaning when they were able to consume 500g of solid feed (46 days), 750g (58 days), and 1000g (63 days).	The results showed that yellow calves had the highest average daily gain (ADG) at weaning, which was 750g (58 days). In addition, rumen microbes (Ruminococcus albus and Ruminococcus flavefacien) reached their highest levels at weaning
Reddy et al., 2017	10-week-old Hanwoo calves fed milk replacer (MR) + concentrate (T1); MR + concentrate + roughage (T2); and MR + concentrate + 30% starch (T3).	The results showed that the MR+ concentrate + 30% starch treatment (T3) significantly increased the highest average daily gain (ADG) by 0.72 kg/day and improved rumen development compared to other treatments.

Table 3: Comparison of Feeding in Post-Weaning Calves.

Referens	Treatment	Result
Ramadan et al., 2025	Fortification of whey concentrate in calf starter at levels of 0%, 2.5%, and 5% in FH dairy calves post-weaning.	Improves feed efficiency and has an impact on farmer income. In addition, it shows better performance along with an increase in Whey Dangke.
Zebeli et al., 2025	Feeding solid feed with varying hay quality, namely high-quality hay (HQH), medium-quality hay (MQH), and concentrate supplementation to weaned Holstein Friesian dairy calves with 4 treatments: treatment 1 = 100% MQH, Treatment 2 = 30% MQH + 70% concentrate, Treatment 3 = 100% HQH, and Treatment 4 = 30% HQH + 70% concentrate.	The results showed that treatment 4 (30% HQH + 70% concentrate) yielded better results than the other treatments, with calves fed HQH exhibiting higher hepatocyte energy status, as indicated by decreased expression of AMP-kinase (AMPK) mRNA, which is a cellular energy sensor. Feeding HQH increased the expression of fatty acid transporter genes and their binding proteins.
Utamy et al., 2025	Feeding green calf starter to post-weaning dairy calves containing 10% indigofera and 12% gliricidia as protein sources compared to conventional feed.	The results showed that post-weaning dairy calves fed green calf starter had a higher ADG compared to conventional feed.
Li et al., 2023	Administration of Corn Silage (CS) to Friesian Holstein dairy calves post-weaning at a level of 0%. 27.2%, 46.5%, 54.8%, dan 67.2% CS DM dari berat badan.	The results showed that feeding CS 27.2% resulted in rapid ADG and rumen development. This indicates that post-weaning dairy calves need fiber intake, but still at an appropriate dose.

of approximately 16–18% is necessary to support tissue accretion and reproductive organ development; however, excessive protein intake may lead to metabolic disorders, such as elevated blood urea concentrations (Susilawati et al., 2023). During the post-weaning stage, β-hydroxybutyrate (BHB) and non-esterified fatty acid (NEFA) levels tend to decline, indicating sufficient energy supply as a result of rumen maturation and increased fermentation of solid feed (Steele et al., 2017). Several studies on the comparison of milk feeding strategies for pre-weaning calves are presented in Table 3.

Targeting metabolic pathways to enhance growth and feed efficiency

Targeting metabolic pathways is a strategic approach to improving growth and feed utilization efficiency in dairy calves. Efficient use of nutrients particularly energy and protein is a fundamental determinant of animal productivity (Nahak et al., 2024). Dairy cattle possess a specialized multi-compartment digestive system consisting of the rumen, reticulum, omasum, and abomasum. The rumen, as the first and largest compartment, functions as a biological fermenter in which microbial communities bacteria, protozoa, and fungi degrade feed components such as cellulose, hemicellulose, starch, and protein. This anaerobic fermentation process produces simple metabolites, primarily volatile fatty acids (VFA), ammonia (NH₃), and metabolic gases such as methane (CH₄) and carbon dioxide (CO₂) (Xu et al., 2021).

Protein and energy are the primary nutritional determinants during the early life stages of dairy calves, exerting a direct influence on growth performance, immune system development, and long-term productive potential (Ghaffari et al., 2025). During the pre-weaning period, calves require substantial amounts of high-quality protein and metabolizable energy to support rapid growth and optimal lean tissue accretion. Although increased dietary protein and energy intake has been shown to enhance body weight gain and feed efficiency (Rauba et al., 2019), excessively high nutrient supply is often constrained by metabolic efficiency. Such inefficiency occurs when protein intake is not adequately balanced with available energy or the animal’s metabolic capacity, resulting in surplus amino acids being oxidized for energy or converted into fat rather than incorporated into body tissues. Consequently, an imbalance in the dietary energy-to-protein ratio reduces nitrogen utilization efficiency and increases non-productive metabolic heat production, ultimately compromising nutritional efficiency (Barzegar et al., 2020).

VFAs acetate, propionate, and butyrate are absorbed across the rumen wall and serve as the animal’s principal energy source. In addition, the rumen is the site of microbial protein synthesis; microbial cells that flow into the small intestine are digested and absorbed as metabolizable protein. The pantothenate and coenzyme A (CoA) biosynthesis pathways play crucial roles in energy metabolism, as well as in the synthesis of milk fat and milk protein, ultimately enhancing milk yield and feed efficiency (James et al., 2024). Branched-chain amino acid pathways valine, leucine, and isoleucine contribute to muscle development and protein metabolism, while nitrogen metabolic pathways are involved in protein recycling and improving nitrogen utilization efficiency (Sammad et al., 2020).

Energy-providing feeds constitute a major component of livestock diets, supplying energy required for maintenance, growth, production, and reproduction. Feed energy is primarily derived from carbohydrates, fats, and partially from proteins, with carbohydrates serving as the main source (Jiang et al., 2024). Common energy-rich feed ingredients include cereal grains such as corn, sorghum, and wheat; agro-industrial by-products such as rice bran, pollard, and molasses; and tuber crops such as cassava and sweet potato. In addition, vegetable oils and animal fats may be used to increase the energy density of rations.

Feed energy values are typically expressed as Total Digestible Nutrients (TDN), Metabolizable Energy (ME), and Net Energy (NE) (Azarfar et al., 2025). High crude fiber content can decrease energy availability due to reduced digestibility; therefore, selecting energy sources must consider the balance between energy content and fiber levels (Acosta et al., 2020). Adequate energy is essential to support metabolic processes, including tissue synthesis, milk production, and reproductive activity. Energy deficiency may lead to reduced performance and metabolic disorders such as ketosis, increasing the risk of Negative Energy Balance (NEB), especially in dairy cows. Conversely, excessive energy intake may induce obesity and reproductive problems (Utamy et al., 2025).

A variety of feed processing technologies including grinding, fermentation, extrusion, and pelleting can enhance energy availability by improving starch and fiber digestibility. Energy-based ration formulation strategies must be aligned with animal requirements, guided by Nasem recommendations, and balanced with protein, vitamins, and minerals. Recent innovations include the use of agro-industrial by-products as alternative energy sources, the application of enzymes and additives to enhance digestibility, and the adoption of energy-efficiency concepts to support sustainable dairy production (Abid et al., 2019).

Energy metabolism in ruminant livestock begins when feed comprising forage containing cellulose and hemicellulose, and concentrates containing starch enters the rumen and is degraded by ruminal bacteria through fermentation. Most carbohydrate-rich feed is metabolized by rumen microbes. The primary products of this fermentation are volatile fatty acids (VFA) acetate, propionate, and butyrate along with by-products such as methane (CH₄) and carbon dioxide (CO₂). VFAs are then absorbed across the rumen epithelium and transported to the liver, where they undergo gluconeogenesis to produce glucose, which is circulated to cells and tissues throughout the body and oxidized into ATP (Beckett et al., 2025).

Energy constitutes the largest nutrient fraction supplied by almost all common feed ingredients used in livestock diets. Sufficient dietary energy is essential to meet maintenance, growth, and production requirements. In addition to energy, optimal growth in livestock is highly dependent on adequate protein availability (Nahak et al., 2024). Therefore, protein is one of the most critical nutrients during the growth phase, alongside energy.

Protein-rich feed ingredients are vital in livestock rations because they serve as substrates for tissue formation, enzyme and hormone synthesis, and metabolic processes that support growth, production, and physiological function (Mariz et al., 2018). In ruminants, dietary protein is degraded by rumen microbes into amino acids and ammonia, which are subsequently utilized to synthesize microbial protein. After passing to the abomasum and small intestine, microbial protein becomes the primary source of absorbable amino acids for the animal (Wang et al., 2015).

Protein sources in animal feed originate from various categories, including plant-based materials, animal products, fermentation products, and leguminous forages. Common plant protein sources include soybean meal, coconut meal, peanut meal, rice bran, and cottonseed meal. Animal-derived protein sources such as fish meal, blood meal, and meat and bone meal generally contain high protein levels with favorable amino acid profiles. Fermentation products like distillers dried grains (DDGS) and yeast cultures are also used as supplemental protein sources. Additionally, legume forages such as Gliricidia sepium, Leucaena leucocephala, and Indigofera species serve as natural protein sources that provide nitrogen for rumen microbes (Salim and Hariyono, 2025).

Crude protein (CP) content varies widely across feed ingredients for instance, soybean meal typically contains 44–48% CP (González et al., 2002), fish meal 55–65%, coconut meal 20–25%, and leguminous forages approximately 18–25% CP (Castro et al., 2019). When selecting protein sources, consideration must be given to protein quality, digestibility, and amino acid balance to ensure alignment with animal requirements. Adequate and high-quality protein intake supports muscle development, milk production, and reproductive function, whereas protein deficiency can impair performance and lead to metabolic disturbances (Kim and Lee, 2021).

Protein plays a key role in livestock growth, particularly in achieving high daily weight gain, which is only possible when dietary protein intake is sufficient (Tahuk et al., 2023). Protein and energy consumption are interdependent because tissue synthesis, body growth, and maintenance of physiological balance rely heavily on the synergy between these nutrients (Aryanto et al., 2013; Tahuk et al., 2016). According to Waldi et al. (2017), dietary protein intake must match animal requirements in order to support microbial protein synthesis in the rumen; an increase in microbial biomass enhances nutrient absorption efficiency. Optimal protein intake improves ruminal fermentation, enabling VFA production to adequately supply maintenance energy needs; surplus energy can then be stored in body reserves, contributing to increases in body weight (Adi et al., 2020).

Concurrently, tissue growth is regulated by a coordinated intracellular signaling cascade in which growth hormone (GH) activates Janus kinase 2 (JAK2), leading to the stimulation of insulin-like growth factor-1 (IGF-1) synthesis in the liver. Circulating IGF-1, together with activation of the mammalian target of rapamycin (mTOR) pathway, functions as a key nutrient-sensing mechanism that responds to the availability of absorbed amino acids, thereby accelerating myofibrillar protein synthesis. This tight coordination between digestive enzymatic efficiency, which governs nutrient availability, and the activation of protein kinase signaling pathways at the cellular level ultimately determines the rate of skeletal and muscle tissue accretion in Friesian Holstein (FH) calves (Wójcik et al., 2018).

Protein metabolism in ruminants involves the degradation of dietary protein and non-protein nitrogen (NPN) in the rumen by microbes into ammonia (NH₃), which is subsequently re-synthesized into microbial protein serving as the primary protein source for the animal. Microorganisms initiate the early stages of protein breakdown in the rumen (Choudhury et al., 2015). A portion of the ammonia that is not utilized by microbial cells is transported to the liver to be converted into urea, which may either be recycled back to the rumen via saliva or excreted in the urine (Nagaraja, 2016).

Meanwhile, protein that escapes ruminal degradation (bypass protein), together with microbial protein, passes into the abomasum where it is digested enzymatically and subsequently absorbed in the small intestine. The absorbed amino acids are then distributed through tissue metabolism to support maintenance functions, muscle accretion, and milk protein synthesis in lactating animals. Nitrogen residues that cannot be utilized by the body are eliminated through feces. The efficiency of microbial protein synthesis is highly dependent on the availability of carbon skeletons from dietary energy and the balance of ammonia concentration in the rumen. Thus, the coordination between protein degradation in the rumen and hepatic urea conversion serves as a key mechanism for fulfilling specific amino acid requirements in ruminant livestock (Lima et al., 2023).

Optimizing metabolic health through phytogenic feed encapsulation

Encapsulation is a process in which a material is coated with another substance (Agnihotri et al., 2012; Agustin and Wibowo, 2021). It is a technology that utilizes polymer-based coatings, which not only act as binding agents but can also enhance the nutritional value of feed (Groza, 2021). Microencapsulation allows controlled release of active compounds at specific target sites (Sitinjak et al., 2025). Phytogenic feed additives also referred to as phytobiotics are plant-derived bioactive compounds incorporated into feed to improve livestock productivity (Windisch et al., 2008). These additives, sourced from medicinal herbs and spices, serve as natural alternatives to synthetic antibiotics and have been shown to enhance performance, digestibility, and weight gain in livestock (Wang et al., 2024).

Phytogenic compounds can improve feed intake by enhancing palatability through improved flavor and aroma, and they also possess antioxidant properties (Yang et al., 2015). Moreover, these compounds can modulate ileal mucosal gene expression and stimulate digestive secretions, thereby improving nutrient digestibility (Yang et al., 2015). Phytogenics may also exert beneficial effects on nutrient utilization by stimulating digestive enzymes such as lipase, amylase, and protease, as well as improving gastrointestinal morphology (Upadhaya and Kim, 2017).

The encapsulation process involves entrapping nutrients within a protective matrix to safeguard them from ruminal degradation (Herlina et al., 2021). This technology enables targeted delivery of sensitive nutrients such as amino acids, vitamins, and minerals to the lower gastrointestinal tract. As a result, nutrient utilization is improved, as demonstrated by the capacity of microencapsulated amino acids to enhance protein synthesis and milk production in dairy cows (Gott et al., 2015). Encapsulated feed additives are also used to improve growth and feed efficiency in beef cattle, with encapsulated essential oils, enzymes, and amino acids incorporated into diets to enhance nutrient utilization and reduce digestive disturbances.

The application of encapsulation technology in ruminant nutrition has been shown to improve nutrient availability, reduce wastage, and enhance animal performance, ultimately contributing to more efficient and sustainable livestock production systems. Encapsulation protects sensitive compounds such as vitamins, minerals, probiotics, and other additives from ruminal degradation, ensuring their availability at the appropriate site of digestion and absorption for optimal health and growth (Garba and Fırıncıoglu, 2023). Furthermore, encapsulation can improve feed efficiency by ensuring nutrients are delivered to regions of the digestive tract where their utilization is maximized, thereby supporting increased weight gain and milk production in ruminants (Temiz and Ozturk, 2018).

In post-calving dairy calves, supplementation with encapsulated calcium butyrate at a dose of 4 kg/ton of feed has been reported to enhance productive performance and shorten the calving interval (Malau-Aduli et al., 2020). Similarly, dietary inclusion of 0.05% biotanical extract combined with 0.3% encapsulated butyrate significantly improved growth performance by approximately 9.4% and stimulated rumen development, thereby accelerating the transition from liquid to solid feed during the weaning period (Liu and Casper, 2022). Although the application of encapsulation technology increases feed production costs, encapsulated compounds such as butyric acid have consistently demonstrated their capacity to enhance animal performance and optimize nutrient utilization. Improved feed efficiency ultimately contributes to higher economic returns, indicating that the use of encapsulated feed additives remains a cost-effective and beneficial strategy in ruminant nutrition.

Nutritional strategies to support metabolic development in dairy calves

Nutritional strategies implemented for dairy calves are closely associated with fulfilling optimal nutrient requirements during the growth phase. Key nutrients including energy, protein, vitamins, and minerals play essential roles in maintaining health, supporting growth, and preparing dairy calves for future reproductive function (Erickson and Kalscheur, 2020). Feeding diets with adequate protein content has been shown to improve growth performance and nitrogen (N) utilization efficiency, particularly during early development (Berends et al., 2015).

According to Ghaffari et al. (2025), one strategic approach to supporting rumen development is the gradual transition from a milk-based diet to solid feed rich in starch and supplemented with balanced forage fiber. This dietary composition stimulates the growth of ruminal papillae and epithelial maturation, thereby enhancing nutrient absorption capacity. High-starch starter feeds promote microbial fermentation and papilla development, whereas forage inclusion serves to stabilize ruminal pH. Processing of cereal grains, such as grinding and steam treatment, is also necessary to improve starch digestibility and energy availability. Collectively, these strategies help maintain the balance between microbial fermentation, rumen health, and optimal growth in dairy calves (Kertz, 2023).

Beyond meeting basic nutritional needs, synchronicity between energy and protein supply must be maintained to support metabolic efficiency and tissue development. An imbalance between the two can impair digestive organ maturation and reduce growth rate. Therefore, starter feed formulation must be designed with an appropriate energy-to-protein ratio to support muscle development and digestive system maturation (Biricik et al., 2006).

Metabolic development is also influenced by the adaptation of rumen microbiota. Transitioning from liquid feed to solid feed should be conducted gradually to prevent digestive disorders, such as subclinical acidosis (Abdela, 2016; Wang et al., 2019). The inclusion of prebiotic- or probiotic-containing feed ingredients can help stabilize the rumen microbial population, enhance fiber fermentation, and maintain gastrointestinal health (Sun et al., 2021). Additionally, the availability of fresh drinking water is crucial, as water is a key component in fermentation and metabolic processes. Water deficiency can reduce starter intake and subsequently impair rumen development, as reflected by a lower fecal consistency score (Wickramasinghe et al., 2019). This effect is primarily mediated through decreased consumption of starter feed, which serves as a concentrated source of fermentable nutrients essential for rumen maturation. Reduced intake of such concentrates limits the production of volatile fatty acids, particularly butyrate, thereby inhibiting ruminal papillae development. Young calves require low-fiber, highly digestible concentrate feeds to effectively stimulate rumen development during the pre-weaning period (Lowe et al., 2022).

In nutritional management, starter-feeding frequency also plays an important role. Providing starter feed ad libitum from an early age accelerates solid feed intake, facilitates milk reduction, and supports ruminal papillae development (Govil et al., 2017). A combination of high-quality starter feed, limited forage, and proper water management creates an ideal environment for metabolic development in dairy calves (Imani et al., 2017).

According to Ramadan et al. (2025), Two months of age represents a critical transition as calves shift from liquid milk to solid starter feed to maintain performance. High-quality starter feed with low fiber content effectively stimulates the development of the reticulo-rumen (Maharani et al., 2015). Recommended starter composition includes 16–20% crude protein (CP), 3% crude fat (CF), 80% total digestible nutrients (TDN), 0.6% calcium (Ca), and 0.4% phosphorus (P) (NASEM, 2021). The composition of calf starter is formulated to meet the evolving physiological and nutritional requirements of calves at different growth stages. During the pre-weaning phase, calves rely entirely on liquid feed, either maternal milk or milk replacer, and therefore do not consume calf starter. As calves enter the weaning phase, calf starter is gradually introduced to facilitate the transition from liquid to solid feed and to support rumen development. Because this period represents a critical phase of rapid growth and ruminal adaptation, calf starter provided during weaning is recommended to contain approximately 18–20% crude protein (CP). In the post-weaning phase, calves increasingly adapt to solid feed intake, and a slightly lower dietary protein level of 16–18% CP is considered sufficient to meet their maintenance and growth requirements.

CONCLUSION

The metabolic development of dairy calves is a complex process that requires an integrated nutritional approach from the pre-weaning through the post-weaning phase. During the pre-weaning period, the primary focus is meeting energy and protein requirements through milk and high-quality starter feed to support early growth and prepare calves for the transition to solid feed. The weaning transition must be implemented gradually, incorporating strategies that stimulate rumen development, maintain energy balance, and prevent metabolic disorders such as acidosis. As calves enter the post-weaning phase, optimizing nutrient utilization becomes a critical priority to support growth, health, and feed efficiency. This approach includes adjusting the energy-to-protein ratio, ensuring adequate water management, and providing limited amounts of forage. Additionally, targeting metabolic pathways through nutritional manipulation and feed additives can enhance metabolic efficiency and growth rate.

Innovative technologies such as phytogenic feed encapsulation offer substantial potential for supporting metabolic health, improving immune function, and optimizing feed performance through controlled release of bioactive compounds. Overall, effective nutritional strategies must consider energy–protein synchronization, rumen microbiota adaptation, and the application of modern nutritional technologies to achieve optimal growth, feed efficiency, and long-term health in dairy cattle. In the future, feed supplements such as phytogenic additives and encapsulated products may be formulated with a range of bioactive compounds that are safe and suitable for calf nutrition. This strategy represents a targeted approach to calf feed modification aimed at enhancing growth performance and promoting optimal rumen development. The use of encapsulation technology, in particular, may improve the stability and bioavailability of active compounds, allowing for more efficient delivery to the gastrointestinal tract while minimizing potential negative effects during early life stages.

ACKNOWLEDGMENTS

The authors wish to extend their profound gratitude to the Dean of the Faculty of Animal Science, Hasanuddin University, as well as to the Dairy Cattle Laboratory of the Faculty of Animal Science, Hasanuddin University, for their invaluable support, assistance, and collaboration in facilitating the successful completion of this study.

NOVELTY STATEMENT

This review contributes novelty by systematically synthesizing recent advancements in nutritional management and metabolic health of dairy calves across the pre-weaning, weaning transition, and post-weaning phases. It bridges established practices such as colostrum management and starter feeding with emerging approaches, including energy–protein synchronization, encapsulation-based feed technologies, and phytogenic additives. By integrating physiological, nutritional, and feed technology perspectives, the review proposes a comprehensive framework elucidating how early-life nutrition and metabolic efficiency influence reproductive preparedness, long-term health trajectories, and sustainable productivity. Consequently, the discussion extends beyond growth-oriented outcomes to emphasize nutrition-based management strategies that support resilience and sustainability in future dairy production systems.

AUTHOR’S CONTRIBUTION

Ikran Ikran and Renny Fatmyah Utamy: Conceived and designed the study, collected data, and wrote the paper; Ambo Ako and Zyahrul Ramadan: Conceived and designed the study and wrote the paper; Irmayanti Irmayanti, Azisah Nurfadilah, and Nur Fajri Muhlis: Wrote the paper.

Funding

The author declares that this study received no financial support from any funding agency or external source.

Ethics statement

This article is a review and does not include any studies involving human participants or animals; hence, ethical approval was not applicable

Generative AI and AI-assisted technology statement

Generative artificial intelligence tools are used for language refinement, such as improving grammar, readability, and clarity of expression. In addition, in searching for the latest references relevant to this study.

Data availability statement

This article is a review and does not involve the generation of new primary data. All data supporting this work are derived from previously published studies that are properly cited in the article

Conflict of interest

The authors have declared no conflict of interest.

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