PJZ_58_5_2015-2024

Introduction

With the improvement of people’s living standards, consumers are increasingly interested in meat from indigenous and local chicken breedss because of desirable and unique taste, rich flavor, and firm texture (Anyona et al., 2023). Moreover, many consumers prefer to purchase free-range products, such as free-range chicken and eggs, et al. It is well known that chickens from free-range systems have better meat quality. Moreover, previous studies have showed that free-range systems were more beneficial to animal health and more in line with animal welfare laws (Yamak et al., 2016).

Different factors are known to influence meat quality, such as slaughter age, breed, sex, management conditions, and diet composition (Kowalski et al., 2024). Research on chickens showed that genotype has a significant effect on the meat quality, fatty acid composition, and consumer preference (Devatkal et al., 2019). Beijing-you chickens had a higher water capacity, as well as lower shear forces and IMF content than Cobb 500 broiler, indicating that the local chickens have better meat quality than commercial chickens (Chen et al., 2023). Sex is also one of the most important factors in chickens, ducks, geese, quails, and turkeys (Śmiecińska et al., 2022; Huang et al., 2023). The meat from females showed a significantly higher protein, dry matter, fiber diameter and shear force and a significantly lower fat level than the male group (Cygan-Szczegielniak and Bogucka, 2021).

Dong’an chicken (DAC) is one of the most important and popular local breeds in China, especially in Hunan Province, and it was recorded as the list of national livestock and poultry genetic resources protection in China in 2010 (Peng et al., 2018). DAC has the characteristics of coarse feeding tolerance, strong adaptability, good stress resistance, and tender and delicious meat. A growing body of scientific research indicated that the indigenous chicken meat has high nutritional value and desirable sensory properties in free-range systems (Baéza et al., 2021). In the future, the genetic diversity of indigenous chickens will be needed to meet production and environmental conditions changes, thereby achieving sustained genetic improvement and promoting rapid adaptation to changing breeding objectives. However, there is limited existing information on sex-related differences in meat composition and quality changes in free-range local chickens. Hence, the objective of this study was to determine the effect of sex on the physicochemical traits, chemical composition, muscle fibers, mineral, amino acids and fatty acids composition of the free-range local chickens.

Materials and Methods

Animals, experimental design and sample collection

The experiment was conducted in the Dong’an chicken Technology Company Limited, Yongzhou, Hunan, China. From March to September. A total of 90 one-day-old DACs (half males and half females) were kept indoors until 10 weeks of age, and from week 11 until slaughter they were divided into 2 groups, according to the sex, and reared under organic conditions. Indoor and outdoor area per bird was 0.5 m2 and 5 m2, respectively. The outdoor access from the pens was provided after 11 weeks of age during daylight hours (from 8:00 am to 5:00 pm), and those chickens were exposed to natural environment (the average temperature was 20-25 ℃). Birds were confined to indoor pens at night. Feed and water were available ad libitum. The birds were fed commercial complete chicken diets: starter (0-9 weeks), grower (10-20 weeks), and finisher (21-28 weeks). The composition of diets fed to DACs different feeding periods is presented in Table I.

On the last day of rearing, thirty-two (16 males and 16 females) DACs with similar body weight were fed for 28 weeks. They were slaughtered by electrical stunning followed by cutting the jugular vein after 12 h feed withdrawal. The breast (pectoralis major) and thigh muscles (peroneus longus) were extracted from the right side of each carcass for meat quality detection.

Measurements of the physicochemical properties

The pH of muscles were determined at 45 min and 24 h postmortem at 2.5 cm depth using a pH meter (pH-STAR, SFK technology, Denmark). Meat color defined as lightness (L*), redness (a*), and yellowness (b*) was determined according to the method given by Jin et al. (2019) using a hand held color meter (CR 410, Minolta, Japan). The average values (pH and meat color) were defined from 3 measured values of the same area.

Table I. Ingredients and chemical composition of the experimental basal diets.

Item1	Age of Dong’an chicken
Item1	10-20 weeks	21-28 weeks
Ingredient (%)
Corn	66.50	62.50
Wheat bran	4.00	3.00
Soybean meal	24.50	24.50
Limestone	1.00	6.00
Premix2	4.00	4.0
Total	100.00	100.00
Calculated composition (%)
ME (MJ/kg)	11.66	11.07
CP	16.38	15.90
Ca	0.97	2.87
AP	0.47	0.46
Lys	0.78	0.75
Met	0.40	0.38
Met+Cys	0.68	0.65

1ME, metabolisable energy; CP, crude protein; Ca, calcium; AP, available phosphorus; Lys, lysine; Met, methionine; Met+Cys, methionine+cysteine. 2Premix provided per kilogram of diet: vitamin A, 250 000 IU; vitamin D3,90 000 IU; vitamin E, 500 IU; vitamin B1, 52 mg; vitamin B2, 180 mg; vitamin B6, 113 mg; vitamin B12, 0.60 mg; vitamin K3, 105 mg; niacin, 738 mg; pantothenic acid, 226 mg; folic acidm, 24 mg; Zn, 3000 mg; Fe, 1500 mg; Mn, 1800 mg; Cu, 240 mg; I, 23 mg; Se, 4.80 mg; Ca, 10.00 g; P, 2.60 g; NaCl, 3.70 g.

The water loss rate (WLR), drip loss (DL), and cooking loss (CL) of muscles were measured 24 h postmortem. The WLR of muscles were determined as described by Weng et al. (2022). The WLR analysis was performed using a dilatometer (C-LM3B, Tenovo, Beijing, China). About 1 g samples were weighed 24 h postmortem (W1). Thereafter, 20 filter papers were placed on the top and bottom of the sample. The sandwich was placed between the hard plastic plates on the platform of the dilatometer. The meat sample was pressurized (35 kg) for 5 min and weighed again (W2). The WLR was calculated using the following equation: WLR (%) = [(W1-W2)/W1] × 100%. The DL of muscles were determined as described previously (Zhang et al., 2015). This sample (3 × 2 × 1 cm) was weighed and recorded as W3, and then hung in a plastic bag in a refrigerator for 24 h at 4°C. After 24 h, the samples were weighed again and recorded as W4. DL was calculated using the following equation: DL (%) = [(W3-W4)/W3] × 100%. The CL of muscles were determined according to Baéza et al. (2021). About 10 g samples (W5) were placed on the steamer of an aluminum steame for 45 min and cooled at room temperature for 35 min, the samples were weighed again and recorded as W6. CL was calculated using the following equation: CL (%) = W6/W5 × 100%.

Measurements of the chemical components

The contents of moisture, crude protein, crude fat, and crude ash of the breast and thigh muscles were analyzed according to the procedures of the Association of Official Analytical Chemists (AOAC, 1995). Crude moisture contents were determined by oven drying at 105°C overnight. Crude protein (N×6.25) contents were measured by the Kjeldahl method with the Kjeltec System 8400 (FOSS NIRSystems Inc., Hillerød, Denmark). Crude fat contents were extracted in a Soxhlet apparatus using petroleum ether (2050, FOSS). Crude ash contents were measured by weight difference before and after converting 5 g of ground muscles to ashes in a muffle furnace (525 ℃).

Measurements of the muscle fiber density and diameter

The muscle fiber density and diameter was determined according to Zhao et al. (2024) and Cardiff et al. (2014). Briefly, muscle samples (1 × 1 × 1 cm) were fixed in 4% paraformaldehyde for more than 48 h, dehydrated in ethanol solutions of 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, and 95%, followed by embedding in paraffin. Histological sections were cut and then stained with hematoxylin-eosin. Three sections of muscle samples from each period were selected with 3 different fields of view for each slice. The cross-sectional area of each muscle fiber separately (μm2) and average diameter (μm) were measured from at least 20 muscle fibers from each field.

Estimation of the mineral content of muscles

Concentrations of iron (Fe), manganese (Mn), zinc (Zn), copper (Cu), selenium (Se), magnesium (Mg), and calcium (Ca) in the muscle samples were estimeted according to the method of Cheng et al. (2017) and Tang et al. (2015). Briefly, the fresh muscle samples were freeze-dried and then crushed. Approximately 2 g of the freeze-dried samples were weighted into the bottom of the digestion tube. Add 5 mL of concentrated nitric acid and 1 mL of hydrogen peroxide (H2O2) to the fume hood using a glass syringe, and then the sample was placed in a microwave digestion instrument. The digestion program was the following: 150 ℃ for 10 min, 180 ℃ for 5 min, and 200 ℃ for 25 min. After the digestion is complete, 0.4 mL of perchloric acid was added followed by ultrapure water in 50 mL volumetric flask to make up to volume. The mineral contents were analyzed by an inductively coupled plasma mass spectrometry (Optimal 2100DV, Perkin-Elmer-Sciex, Norwalk, NY, USA).

Determination of the muscle composition of hydrolyzed amino acid and fatty acid

The muscle samples were first completely dried in a freeze dryer. The method of the muscle composition of free amino acid and fatty acid was referred to the previous studies (Liu et al., 2021; Folch et al., 1957). About 0.5 g freeze-dried samples were weighed and mixed with 5 mL of 0.01 mol/L hydrochloric acid for preparation of homogenate, and then centrifuged at 5000 r/min-1 for 5 min. Then, 0.5 mL of the supernatant was mixed with 8% salicylic acid at 4 ℃ for 12 h. The mixture was centrifuged twice at 12000 r/min-1 for 10 min. The supernatants were used for estimation of amino acids in automatic amino acid analyzer (L-8900, Hitachi, Tokyo, Japan).

The muscle contents of fatty acids were determined using an Agilent 7890 N gas chromatography equipped with a flame ionisation detector (Agilent Technologies, Santa Clara, CA, USA) and a CP-Sil 88 fused silica open tube capillary column (100 m × 0.25 nm; Agilent Technologies, USA) based on the retention time and peak area of each fatty acid. About 0.2 g freeze-dried samples were weighed and placed in a hydrolysis tube, to which 4 mL of chloroacetyl methanol solution, 1 mL 1.0 mg/mL-1 C11:0 internal standard solution, and 1 mL of n-hexane in sequence were added. The bottle was capped and placed in an 80 ℃ water bath for 2 h. After cooling, 5 mL of 7% potassium carbonate solution were added and shake well. Centrifuged for 5 min at 1000 r/min-1, filterd with a 0.2 µm membrane, and performed machine testing. The temperature of the syringe and detector were 260 ℃ and 270 ℃, respectively. The gas carrier is He (2.0 mL/min-1), using a split flow syringe with a split ratio of 30:1. Saturated fatty acid (SFA) total proportion was the weighted percentage sum of myristic (C14:0), palmitic (C16:0), margaric (C17:0), stearic (C18:0), and eicosanoic (C20:0) acid. Total proportions of monounsaturated fatty acids (MUFA) included palmitoleic (C16:1), oleic (C18:1), eicosenoic (C20:1) acid. Additionally, the polyunsaturated fatty acid (PUFA) total percent summed linoleic (C18:2), linoleic (C18:3n6), α-linoleic (C18:3n3), dihomo-c-linolenic (C20:3n6), arachidonic(C20:4n6), and docosahexaenoic(C22:6n) acid.

Statistical analysis

Data were analyzed by t-test using SPSS Statistics software (version 21.0; IBM-SPSS Inc., Chicago, IL, USA) and expressed as means ± standard error of mean (SEM). Differences were considered significant at P < 0.05.

Results

Effect of sex on physicochemical traits of DAC

The physicochemical traits in breast and thigh muscles of DACs are shown in Table II. The redness (a*) and pH45min values of breast muscle and the CL of thigh muscle were significantly higher (P < 0.05) in males than in females. The yellowness values (b*24h) of thigh muscle and the WLR of breast muscle were markedly lower (P < 0.05) in males than in females. There were no significant differences (P > 0.05) in other traits between them.

Effect of sex on chemical composition and muscle fibers of DAC

The chemical composition and muscle fibers in breast and thigh muscles of DAC are reported in Table III and Figure 1. The crude fat content of breast and thigh muscle and the crude ash content of breast muscle were significantly lower (P < 0.05) in males than in females. The moisture content and muscle fiber density of thigh muscle were significantly higher (P < 0.05) in males than in females.

Effect of sex on mineral contents of DAC

Sex had no effect (P > 0.05) on the minerals contents in breast and thigh muscles of DAC (Table IV).

Effect of sex on hydrolyze amino acids profile of DAC

The hydrolyze amino acids composition in breast and thigh muscles of DAC are presented in Table V. The contents of Gly, Ala, and Pro of thigh muscle were significantly higher in males than in females (P < 0.05).

Table II. Effects of sex on physicochemical traits in breast and thigh muscles of Dong’an chicken1.

Items3		Breast muscle2				Thigh muscle2
Items3		Male	Female	SEM	p-Value	Male	Female	SEM	p-Value
pH45min		6.20a	6.01b	0.11	0.032	6.00	6.02	0.08	0.332
pH24h		5.77	5.69	0.10	0.315	5.73	5.81	0.11	0.378
Color45min	L*	48.10	48.69	1.80	0.278	38.48	39.06	2.40	0.224
	a*	8.44a	5.10b	1.01	0.015	18.73	19.75	2.31	0.158
	b*	9.90	8.03	1.73	0.478	7.30b	8.85a	0.52	0.041
Color24h	L*	50.70	52.42	2.29	0.398	43.59	43.89	2.68	0.247
	a*	8.96a	6.51b	1.25	0.029	15.86	16.07	3.09	0.355
	b*	13.90	14.00	1.76	0.193	9.54	10.88	2.71	0.295
WLR (%)		20.50b	27.36a	2.99	0.017	21.05	22.15	3.85	0.572
DL (%)		4.73	5.55	1.06	0.229	3.82	4.79	1.02	0.111
CL (%)		67.13	64.41	3.87	0.063	61.07a	57.47b	1.60	0.027

1Data are means of 16 chickens per group. 2a,b Values with different superscripts in the same row differ significantly (P < 0.05). 3WLR, water loss rate; DL, drip loss; CL, cooking loss.

Table III. Effects of sex on chemical composition and muscle fibers in breast and thigh muscles of Dong’an chicken1.

Items	Breast muscle2				Thigh muscle2
Items	Male	Female	SEM	p-Value	Male	Female	SEM	p-Value
Moisture (%)	71.66	70.73	0.49	0.107	73.47a	71.57b	0.60	0.012
Crude protein (%)	24.87	25.28	0.37	0.288	21.24	21.79	0.58	0.359
Crude fat (%)	0.61b	1.31a	0.26	0.021	2.22b	3.55a	0.61	0.047
Crude ash (%)	1.49b	2.37a	0.11	0.011	1.99	2.03	0.14	0.279
Muscle fiber diameter (μm)	22.49	23.45	1.23	0.521	20.10	21.58	1.01	0.225
Muscle fiber density (number/mm2)	866.62	816.15	48.51	0.117	927.51a	875.11b	48.12	0.041

1Data are means of 16 chickens per group. 2a,b Values with different superscripts in the same row differ significantly (P < 0.05).

Table IV. Effects of sex on selected minerals, inosinic acid and cholesterol contents in breast and thigh muscles of Dong’an chicken (wet tissue basis)1.

Items2	Breast muscle				Thigh muscle
Items2	Male	Female	SEM	p Value	Male	Female	SEM	p-Value
Fe (mg/100g)	2.73	3.32	1.77	0.329	2.85	4.31	1.65	0.479
Mn (mg/100g)	0.08	0.06	0.02	0.158	0.10	0.07	0.03	0.372
Zn (mg/100g)	0.98	0.71	0.32	0.118	1.66	1.49	0.52	0.274
Cu (mg/100g)	0.06	0.08	0.05	0.318	0.05	0.07	0.02	0.372
Se (μg/100g)	31.53	31.94	8.13	0.527	32.92	32.90	8.52	0.163
Mg (mg/100g)	28.65	27.97	3.83	0.119	32.47	28.98	3.15	0.332
Ca (mg/100g)	8.64	8.73	0.49	0.158	7.26	6.95	0.53	0.521

1Data are means of 16 chickens per group. 2Fe, Iron; Mn, Manganese; Zn, Zinc; Cu, Copper; Se, Selenium; Mg, Magnesium; Ca, calcium.

Table V. Effects of sex on hydrolyzed amino acids composition in breast and thigh muscles of Dong’an chicken (mg/g)1.

Items3	Breast muscle2				Thigh muscle2
Items3	Male	Female	SEM	p Value	Male	Female	SEM	p Value
His	31.02	32.24	1.90	0.556	20.57	20.14	0.31	0.236
Ser	34.25	33.35	3.92	0.829	33.34	29.68	1.90	0.126
Arg	50.66	49.10	1.01	0.199	48.62	45.72	1.37	0.101
Gly	36.31	35.44	3.05	0.790	38.27a	33.39b	1.45	0.028
Asp	74.85	74.01	1.79	0.663	71.81	69.30	2.02	0.282
Glu	117.13	115.64	2.99	0.644	117.50	112.39	2.65	0.127
Thr	35.30	34.91	1.06	0.734	34.02	32.21	0.91	0.118
Ala	45.75	44.52	1.31	0.402	44.17a	40.57b	1.21	0.041
Pro	28.29	27.56	0.80	0.417	30.39a	27.84b	0.80	0.033
Cys	4.00	3.95	0.11	0.663	3.38	3.47	0.27	0.766
Lys	68.32	68.22	1.30	0.939	64.32	62.52	1.38	0.261
Tyr	25.13	25.54	2.06	0.854	23.37	22.90	0.95	0.648
Met	17.47	17.75	1.03	0.802	13.99	12.52	2.19	0.539
Val	40.67	40.27	1.17	0.750	36.98	35.25	0.78	0.091
Ile	37.49	37.26	1.05	0.836	34.78	33.31	0.81	0.144
Leu	62.61	62.22	1.43	0.795	59.40	57.02	1.27	0.135
Phe	30.87	31.06	1.10	0.869	29.81	28.44	0.62	0.092
EAA	292.74	291.69	7.47	0.895	273.31	261.27	6.52	0.139
TAA	740.13	733.03	21.85	0.762	704.73	666.68	17.53	0.096
EAA/ TAA(%)	39.56	39.80	0.45	0.617	38.79	39.19	0.22	0.142

1Data are means of 16 chickens per group. 2a,b Values with different superscripts in the same row differ significantly (P< 0.05). 3His, Histidine; Ser, Serine; Arg, Arginine; Gly, Glycine; Asp, Aspartic; Glu, Glutamic; Thr, Threonine; Ala, Alanine; Pro, Proline; Cys, Cystine; Lys, Lysine; Tyr, Tyrosine; Met, Methionine; Val, Valine; Ile, Isoleucine; Leu, Leucine; Phe, Phenylalanine; TAA, total amino acid; EAA, essential amino acid = Thr+Lys+Met+Phe+Ile+Leu+Val.

Table VI. Effects of sex on fatty acids content (% of total acids) in breast and thigh muscles of Dong’an chicken1.

Items3	Breast muscle2				Thigh muscle2
Items3	Male	Female	SEM	p-Value	Male	Female	SEM	p-Value
C14:0	0.38b	0.60a	0.06	0.010	0.53b	0.73a	0.06	0.012
C16:0	25.88	26.11	0.89	0.806	21.42b	24.40a	1.04	0.028
C16:1	1.37	3.00	0.72	0.065	3.20	3.99	0.54	0.197
C17:0	0.28	0.25	0.04	0.400	0.27	0.28	0.02	0.620
C18:0	15.77a	11.24b	1.33	0.014	14.33a	11.70b	0.38	0.000
C18:1	22.11b	33.50a	2.26	0.002	26.90b	31.82a	1.30	0.019
C18:2	16.49	16.76	2.46	0.915	22.16	19.31	1.79	0.164
C20:0	0.11	0.10	0.04	0.687	0.14a	0.11b	0.01	0.022
C18:3n6	0.07	0.11	0.01	0.052	0.12	0.12	0.01	0.705
C20:1	0.23	0.30	0.08	0.453	0.39	0.31	0.04	0.115
C18:3n3	0.38	0.61	0.17	0.219	0.70	0.68	0.11	0.846
C20:3n6	0.76a	0.35b	0.09	0.004	0.45a	0.32b	0.03	0.023
C20:4n6	13.11	6.05	3.02	0.058	7.64a	5.45b	0.27	0.000
C22:6n	3.06a	1.04b	0.59	0.014	1.78a	0.79b	0.26	0.008
SFA4	42.42a	38.29b	1.21	0.028	36.67	37.22	1.60	0.213
MUFA4	23.71b	36.79a	1.09	0.015	30.49b	36.13a	2.34	0.009
PUFA4	33.87a	24.92b	2.96	0.004	32.84a	26.66b	1.96	0.020

1Data are means of 16 chickens per group. 2a,b Values with different superscripts in the same row differ significantly (P < 0.05). 3C14:0-myristic; C16:0-palmitic, C17:0-margaric; C18:0-stearic, C20:0-eicosanoic; C16:1-palmitoleic, C18:1-oleic, C20:1-eicosenoic; C18:2-linoleic, C18:3n6-linoleic, C18:3n3-α-linoleic, C20:3n6-dihomo-c-linolenic, C20:4n6-arachidonic, C22:6n-docosahexaenoic. 4SFA, saturated fatty acid = C14:0+C16:0+C17:0+C18:0+C20:0; MUFA, monounsaturated fatty acids = C16:1+C18:1+C20:1; PUFA, polyunsaturated fatty acid = C18:2+C18:3n6+C18:3n3+C20:3n6+C20:4n6+C22:6n.

Effect of sex on fatty acids profile of DAC

The fatty acids composition in the breast and thigh muscles of DAC are shown in Table VI. The content of SFA in breast muscle and the content of PUFA in breast and thigh muscles were significantly higher in males than in females (P < 0.05). However, the content of MUFA in breast and thigh muscles was significantly lower in males than in females (P < 0.05). The C18:0, C20:3n6 and C22:6n contents in breast and thigh muscles, and the C20:0 and C20:4n6 contents in thigh muscle were significantly higher in males than in females (P < 0.05). The C14:0 and C18:1 contents in breast and thigh muscles were significantly lower in males than in females (P < 0.05).

DISCUSSION

The relatively high value of a* for male in breat muscle could be attributed to the physical activity of the males. A higher level of physical activity promotes an increase in the content of myoglobin, which is directly related to a greater value of redness (Gálvez et al., 2020). The value of b* was higher on female thigh muscle. The result was in agreement with the result of previous studies in chickens (Mosca et al., 2018). However, other researchers found that sex had no effect on meat color (Villegas-Cayllahua et al., 2025). Differences in meat color may be attributed to many factors such as heme pigments, moisture content, sex, strain, protein physical status, and stress (Dai et al., 2024).

In our study, pH was also affected by sex. After harvesting, postmortem glycolysis is activated and accumulation of lactic acid in the muscle is increased, which results in a decline in pH (López et al., 2011). The reduced pH indicated normal glycolysis in the muscle tissue after slaughter. In our study, the value of the pH45 min for breast muscles was significantly higher in males than in females. Our results did not match those of Hussein et al. (2019), who reported that female breast muscles had higher pH than males. The differences in pH values in chicken muscles may be attributed to stress, slaughter weights, chicken genotype, slaughtering method, and glycogen reserves at slaughter (Glamoclija et al., 2015). However, sex did not influence the pH measured at 24 h postmortem. Similar findings were reported by Goo et al. (2019), and Uhlířová et al. (2018), who studied the non-significant effects of sex on carcass pH24h.

Water loss rate is generally used to measure the water-holding capacity. A lower water-holding capacity in muscles can lead to the loss of nutrients and flavor, resulting in a decline in meat quality (Bai et al., 2022). In the present study, we found that the sex of DAC has a significant impact on the water loss rate of the breast muscles and was lower in males than in females, indicating a greater water-holding capacity and better meat quality in males. The current result was corroborated by Damaziak et al. (2014), who reported that muscles of male turkeys had higher water-holding capacity than those of females. We showed that higher CL for male in thigh muscle, and these results were comfirmed by Musundire et al. (2017), who found that males had a higher CL than females.

A comparative analys is of the chemical composition of meat from indigenous and commercial chickens, performed by Weng et al. (2022), confirmed the characteristics of high protein content and low fat content of indigenous chicken. The chemical composition of DAC meat confirms this result being characterized by high protein and low fat contents compared to the standard broiler meat. Sex has a significant effect on the chemical composition of breast and thigh meat. In the present study, females exhibited higher crude fat content of breast and thigh muscles than males, which is in accordance with Pornanek and Phoemchalard (2020). In addition, breast muscle from female had higher crude ash content. The current result was corroborated by Chodová et al. (2021), who reported that crude ash content was affected by sex, with higher values in females than in males. Sex affected myofibrillar fragmentation index and muscle tenderness values of broiler chickens (Hussein et al., 2019). Sex had a significant effect on the diameters of type IIA (red fibers) and type IIB (white fibers) muscle fibers of the wild-living mallards (Janiszewski et al., 2018). In the current study, sex effects were clear for muscle fiber density, where male muscles had higher values than those recorded for female. There is a close relationship between muscle fibers, lipid content, and physical properties. The type and quantity of muscle fibers directly affect the physical properties and functions of muscles, while lipid content indirectly affects their performance by affecting the composition of muscles. Regarding meat quality, an increase in muscle fiber density corresponded to meat with CL and a lower b* value in thigh muscle from male.

Amino acids are the key constituents of protein, and play an important role in optimizing animal production and human nutrition. It is beneficial to the scientific advancement to analyze the amino acid profiles of indigenous chicken. According to the ideal protein model recommended by FAO/WHO, the EAA/TAA proportion of high-quality protein is about 40% (Yuan et al., 2019). Our results showed that the EAA/TAA proportion of breast and thigh muscles are close to 40%, which indicated that DAC could provide good quality protein for human. Glutamic acid, aspartic acid, lysine acid, and leucine acid are the most abundant amino acid in other indigenous chicken (Zhao et al., 2011) and this corresponds to the results of this study. The composition and content of amino acids are important factors that affect the flavor of meat. In the present study, a minor effect of sex on amino acid content was reported for the muscle of DAC, and this result is consistent with no significant difference in inosinic acid content. Some studies also found that sex had no significant effect on the content of amino acid in other domestic species (Boz et al., 2019). In addition to fat content, more interest has been placed on fat quality, i.e., fatty acid composition. Saturated fatty acids are known to contribute to cardiovascular diseases and their intake should not exceed 10% (Kelava et al., 2020). Considering SFA, the highest concentration was found for C16:0, and it was significantly higher in the thigh muscle from female. Besides, the contents of C18:0 and C20:0 were higher on male breast and thigh muscle. With respect to MUFA, the highest concentration was measured for C18:1, and it was significantly higher in the breast and thigh muscle from female. The current result was corroborated by Onk et al. (2019), who reported that the breast meat of the female ducks contained higher proportions of C18:1 than male ducks. These results led to higher total SFA and lower total MUFA contents in male compared with females, which is in accordance with Yu et al. (2020). Considering PUFA, the highest concentration was found for C18:2. There were no statistically significant differences between the meat samples from male and female chickens in the content of this acid, which is in line with the studies Yu et al. (2020) reported that sex had no significant effect on the content of C18:2 in breast and thigh muscles of goslings and adult geese. However, the PUFA content was significantly higher in the breast and thigh muscle from male, which is mainly due to the significant increase of C20:3n6 and C22:6n contents. The current result was corroborated by Kowalska et al. (2020). Therefore, the current result was corroborated by Baeza et al. (2010), who reported that the MUFA percentage was higher and PUFA percentage was lower for the females than for males. These fatty acids are mainly stored in adipose tissue under triglyceride form, while the fatty acids of triacylglycerol are made up mainly of SFA and MUFA. The results indicated that females synthesising lipids earlier than males also deposited more MUFA than males. In additon, sex has a greater impact on fatty acids composition compared to amino acids composition in meat of DAC.

CONCLUSION

It was concluded that sex has an impact on meat quality of DAC. The male exhibited a higher CL, muscle fiber density, amino acids (Gly, Ala, Pro), and PUFA contents in the thigh muscle, and had a lower WLR, crude fat, and MUFA content in the breast muscle. Further research is required to explore the molecular mechanism of sex affecting meat quality.

Declarations

Acknowledgements

We thank all the members who participated in this study for their support and the experimental site keepers for their help.

Funding

This work was supported by the Scientific Research Foundation of Hunan Provincial Education Department, China (24B0649) and Natural Science Foundation of Hunan Province, China (2023JJ40097).

Ethical statement

The author declares that the sampling of the species under investigation was conducted in accordance with the international conventions on the use of animals in scientific research.

IRB approval

The study was approved by the Ethics Committee of Hengyang Normal University (Permit No. HNU-12).

Generative AI and AI-assisted technology statement

The authors declare that no genrative AI was used in the creation of this manuscript.

Statements of conflicts of interest

The authors have declared no conflict of interest.

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