Dietary Supplementation of Glutamine Improves Metabolic Functions in 1-14 Days Old Broilers Under Cold Stress

Haoneng Guo1,2, Shuangshuang Xiao3, Wenfang Lou1,2, Rifat Ullah Khan4, Juanjuan Wu1,2, Bo Huang2, Sifa Dai2,3* and Guanhong Li1*

1College of Animal Science and Technology, Jiangxi Agriculture University, Nanchang 330045, PR China

2Department of Pharmaceutical and Life Sciences, Jiujiang University, Jiujiang 332005, PR China

3College of Animal Science, Anhui Science and Technology University, Fengyang 233100, PR China

4College of Veterinary Sciences, Faculty of Animal Husbandry and Veterinary Sciences, The University of Agriculture, Peshawar 25000, Pakistan

Haoneng Guo and Shuangshuang Xiao contributed equally to this work.

ABSTRACT

The purpose of this experiment is to study the effect of glutamine (Gln) on the metabolic functions of cold stress chicks (1-14 days old) from the perspective of serum biochemical indicators. A total of 192 healthy 1-day-old broilers with no significant difference in weight, were randomly divided into four groups, each group with four replicates and 12 broilers per replicate. Group Ⅰ was a control group, the broilers were fed the basal diet, and the broilers in Group II, III, IV were fed a basal diet supplemented with 1.0% and 1.5%, respectively 2.0% Gln. The broilers were kept at 25±2 ℃ for 14 days. Samples were taken and analyzed at 7 and 14 days of age. On the 7th day, compared with group Ⅰ, the serum level of LDH in group II, III and IV were significantly decreased. Serum triiodothyronine content in group II, III, and IV was significantly increased. Also, compared with the control, the glucose level was significantly decreased in group II, and the serum uric acid content in II, III, and IV was significantly decreased. On the 14th day, compared with group Ⅰ, the K+ in the group III and IV decreased significantly, and the P3+ in the group II and IV decreased significantly. The LDH level in group IV was significantly reduced, and the AST level in group II was significantly reduced. The albumin and globulin levels in group IV were decreased significantly. Under this experimental condition, adding Gln to the diet has a certain improvement effects on serum biochemical indices of cold stressed chicks.

Article Information

Received 14 September 2022

Revised 22 October 2022

Accepted 18 November 2022

Available online 10 March 2023

(early access)

Published 02 May 2024

Authors’ Contribution

HG and SX conducted the experiment. WL, RUK edited the paper. JW, BH sampling and analysis. SD, GL supervision, fund acquisition, editing and writing.

Key words

Glutamine, Chicks, Cold stress, Serum biochemical indices, Serum ions

DOI: https://dx.doi.org/10.17582/journal.pjz/20180827080848

* Corresponding author: daisifa-004@163.com, liguanh@163.com

0030-9923/2024/0003-1433 $ 9.00/0

Copyright 2024 by the authors. Licensee Zoological Society of Pakistan.

This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

INTRODUCTION

In the winter, in most parts of China, the outdoor temperature may be below 0 ℃. In general, cold stress can occur when the temperature is below the optimal living standard for chicks. When chicks suffer from cold stress, the body needs to consume a lot of energy to maintain body temperature to resist the external low-temperature environment, only relatively little energy is used for production and maintenance (Zhang et al., 2016), resulting in reduced growth performance (Hu et al., 2021) and even death. At the same time, cold stress usually causes physiological and biochemical changes in poultry blood (Hangalapura et al., 2006; Wang and Xu, 2008), so it is of great significance for broiler breeding to solve or relieve cold stress of chicks. Cold stress reduces the incubation efficiency of laying hens, and the weight of chicks hatched at normal temperature was significantly higher than under cold stress (Kamanli et al., 2015). Wang and Xu (2008) showed that the weight gain of pheasants in the cold stress group decreased significantly and feed efficiency increased significantly within one week.

Glutamine (Gln) is added to the chickens diet resulted in improved body weight and feed conversion ratio (Zulkifli et al., 2016). Other studies have shown that the addition of Gln in the diet of broilers led to a significant increase in body weight and immune organ weight (Szabó et al., 2014). Yi et al. (2005) also demonstrated a promoting effect of Gln on the growth performance of broilers at a later stage. Studies have shown that Gln can alleviate the effects of heat stress on the growth performance of broilers and improve their serum physiological and biochemical indices (Dai et al., 2012; Hu et al., 2016). Previous studies have shown that different content of Gln can significantly improve the performance and immune organ index of 1-14 days old chicks (Xiao et al., 2019). However, there are few reports on the effects of Gln on serum biochemical indices of cold stress chicks. The aim of the present study was to evaluate the effect of Gln on the serum biochemical parameters in the first two weeks of the broiler chickens under cold stress.

MATERIALS AND METHODS

Test materials

L-glutamine (L-Gln) was purchased from Amresco, USA having purity > 99.0 %. Automatic Biochemical Analyzer and centrifuge were purchased from HATTIECS, Federal Republic of Germany.

Animals husbandry and experimental design

A total of 192 healthy, 1-day old Arbor Acres (AA) broilers were randomly divided into four groups (four replicates in each group and 12 chicks in each replicate), with group I as the control group fed with Gln-free basic diet, and groups II, III and IV fed with 1.0, 1.5 and 2.0 Gln, respectively. The temperature and humidity of the chicken coops were controlled by heaters and humidifiers, and the temperature was maintained at 25±2 ℃ and the humidity was maintained at 60% to 70% for 14 days.

Feeding management and diet formulation

Three days before the start of the experiment, the chicken house was cleaned, fumigated and disinfected. Broilers were fed and watered freely. Immunization was carried out according to broiler husbandry regulations. Daily observation of feed consumption, faeces composition and health condition of the chickens was carried out. The basic diet was corn-soybean meal, which was designed according to the recommendation of National Research Council (1994) (Table I).

Sampling and measurement of indicators

At 7 and 14 days of the experiment, two healthy chicks were randomly selected from each replicate after a 12 h fast, and then slaughtered and sampled. Blood was collected from the carotid artery of the broiler and centrifuged in a 10 ml tube at 3000 r/min for 10 min, then the serum was divided into 0.5 ml tubes and stored at -20℃.

 

Table I. Ingredients and calculated component (g/kg) of basic diet for chicks (1-14 days old).

Daily diet
Ingredients
Corn	600.00
Soybean meal	330.00
Fish meal	20.00
Vit & min permix1	50.00
Calculated component
AME (MJ/kg)	115.50
Crude protein	215.70
Dig. Lys	11.40
Dig. Met	3.50
Calcuim	9.60
Total P	5.70

 

1supplied per kilogram of diet: Vitamin A, 46.29 mg; Vitamin B1, 30 mg; Vitamin B2, 160 mg, Vitamin B6, 50 mg; Vitamin B12, 0.22 mg; Vitamin D, 0.625 mg; Vitamin E, 1.76 mg; Vitamin K, 44 mg; folic acid, 18 mg; niacin, 880 mg; biotin, 2.2 mg; choline, 11 000 mg; zinc, 1 600 mg; iron, 1 600 mg; manganese, 1 600 mg; cuprum, 160 mg; iodine, 7 mg; selenium, 3 mg.

 

Hitachi 7600 Automatic Biochemical Analyzer was used to measure serum biochemical indicators, namely potassium ion (K+), sodium ion (Na+), chloride ion (Cl-), calcium ion (Ca2+), phosphorus ion (P3+), alanine aminotransferase (ALT), aspartate aminotransferase (AST), lactate dehydrogenase (LDH), creatine kinase (CK), triiodothyronine (T3), thyroxine (T4), albumin (ALB), globulin (GLB), glucose (GLU), triglyceride (TG), and uric acid (UA) with the help of commercial assay kits (Nanjing Jiancheng Biotechnology Research Institute, Nanjing, China).

Statistical analysis of data

Data were analyzed under one-way analysis of variance (ANOVA) using SPSS 18.0. Means were separated by using Tukey test. The results were expressed as means±SEM, and P<0.05 was considered as point of significance.

RESULTS

Effect of glutamine on serum antioxidant ability of cold-stressed chicks

The effect of Gln on serum ions of cold stressed broilers on day 7 and 14 are given in Table II. No significance (P>0.05) difference was found in serum K+, Na+, Cl-, and P3 during the first 7 days of the experiment. Serum Ca2+ was significantly (P<0.05) higher in group IV compared to the control. On day 14, serum K+ and P3+ were significantly (P<0.05) lower in group IV compared to the control. The rest of the ions did not change significantly (P>0.05) between the control and the treatments.

 

Table II. Effects of glutamine on serum ions content (mmol/L) of cold-stressed chicks.

	Control	Group II	Group III	Group IV
After 7 d
K+	6.41±0.28	6.42±0.25	6.28±0.18	6.37±0.30
Na+	139.45±2.97	136.48±1.12	138.40±2.01	134.80±2.69
Cl-	108.88±2.41	107.85±1.04	108.43±2.06	104.50±1.95
Ca2+	1.99±0.08b	2.06±0.08ab	2.17±0.03ab	2.20±0.06a
P3+	2.34±0.13	2.35±0.19	2.39±0.07	2.29±0.05
After 14 d
K+	5.72±0.34a	5.23±0.05ab	4.99±0.17bc	4.52±0.31c
Na+	144.58±2.02	141.00±4.57	138.50±1.66	135.48±3.13
Cl-	111.58±1.93	109.25±3.74	107.63±2.26	104.83±3.44
Ca2+	2.22±0.04	2.12±0.04	2.20±0.04	2.09±0.05
P3+	2.82±0.12a	2.36±0.18b	2.49±0.09ab	2.32±0.07b

 

a-b means with different superscripts within each row differ significantly (P<0.05). Control fed a basal diet. Group II fed a basal diet supplemented with 1.0% Gln. Group III fed a basal diet supplemented with 1.5% Gln. Group IV fed a basal diet supplemented with 2.0% Gln. Each value represents mean of four replicate pens of two chicks each (n=8).

 

Effect of glutamine on serum enzymes activities

The effect of Gln on serum ALT, AST, LDH, and CK on day 7 and 14 are given in Table III. Serum LDH content decreased significantly (P<0.05) in the treatment groups compared to the control. No significant changes were recorded in other parameters on day 7.

On day 14, serum AST decreased significantly (P<0.05) in group II compared to the control. Similarly, LDH was also reduced significantly (P<0.05) in group IV compared to control.

Effect of glutamine on serum hormones contents

Compared with control, serum triiodothyronine level content in group II, III, and IV was significantly increased (P<0.05) on the 7th day of the experiment (Table IV).

Effect of glutamine on serum protein content

Table V shows us that on the 14th day, albumin and globulin decreased significantly (P<0.05) in group IV compared to the control.

 

Table III. Effects of glutamine on serum enzyme activity (U/L) of cold-stressed chicks.

	Control	Group II	Group III	Group IV
After 7 d
ALT	1.50± 0.29	1.50± 0.29	2.00± 0.41	1.75± 0.25
AST	251.00± 10.21	220.25± 11.54	235.50± 23.93	229.50± 7.14
LDH	1728.25± 127.72a	1318.50± 144.50b	1214.00± 42.44b	1355.25± 58.36b
CK	2690.50± 284.96	2322.00± 219.87	2068.25± 330.05	2179.25± 49.74
After 14 d
ALT	3.25± 0.25	2.75± 0.48	2.25± 0.25	2.25± 0.48
AST	277.50± 13.49a	244.00± 12.23b	269.67± 4.91ab	249.00± 8.34ab
LDH	1828.25± 163.41a	1534.25± 154.13ab	1806.50± 146.71ab	1352.00± 149.67b
CK	2769.75± 208.18	2564.00± 280.18	2816.00± 400.61	2704.33± 429.87

 

a-b for statistical details and for details of groups see Table II. ALT, alanine aminotransferase; AST, aspartate aminotransferase; LDH, lactate dehydrogenase; CK, creatine kinase.

 

Table IV. Effects of glutamine on serum hormone levels (nmol/L) of cold-stressed chicks.

	Control	Group II	Group III	Group IV
After 7 d
T3	1.40±0.20	2.03±0.36	1.75±0.20	1.72±0.19
T4	16.76±2.90	17.67±2.26	18.26±1.08	17.36±2.15
After 14 d
T3	1.43±0.35	1.80±0.21	1.67±0.24	1.41±0.25
T4	18.45±1.93	18.09±0.80	19.11±2.26	19.74±3.23

 

For statistical details and for details of groups see Table II. T3, triiodothyronine; T4, thyroxine.

 

Table V. Effects of glutamine on serum protein content (g/L) of cold-stressed chicks.

	Control	Group II	Group III	Group IV
After 7 d
ALB	10.20±0.46	10.20±0.67	11.27±0.53	10.35±0.64
GLB	14.20±0.17	14.27±0.79	15.55±0.40	14.45±0.77
A/G	0.72±0.04	0.72±0.04	0.72±0.03	0.72±0.03
After 14 d
ALB	12.37±0.21a	10.55±0.49ab	12.00±0.33a	9.90±1.02b
GLB	14.57±0.44a	12.82±0.39ab	14.35±0.84a	12.15±0.97b
A/G	0.85±0.01	0.82±0.02	0.84±0.04	0.81±0.04

 

a-b for statistical details and for details of groups see Table II. ALB, albumin; GLB, globulin; A/G, calculate as albumin to globulin.

 

Table VI. Effects of glutamine on serum GLU, TG, and UA levels (mmol/L) of cold-stressed chicks.

	Control	Group II	Group III	Group IV
After 7 d
GLU	11.49±0.63a	9.48±0.72b	10.99±0.54ab	9.68±0.45ab
TG	0.40±0.06	0.33±0.08	0.33±0.04	0.34±0.01
UA	577.00± 57.37a	284.50± 7.24c	430.25± 24.52b	425.00± 64.24b
After 14 d
GLU	9.72±0.31	10.51±0.80	10.72±0.56	9.58±0.18
TG	0.43±0.04	0.31±0.05	0.32±0.03	0.42±0.12
UA	585.33± 36.67a	303.25± 44.05b	360.00± 53.06b	542.33± 30.99a

 

a-b for statistical details and for details of groups see Table II. GLU, glucose; TG, triglyceride; UA, uric acid.

 

Effect of glutamine on serum glucose (GLU), triglyceride (TG) and uric acid (UA) contents

On the 7th day, compared with control, the GLU level was significantly decreased in group II (P<0.05). The serum UA content in group II was significantly (P<0.05) lower compared to the control. The concentration of UA decreased significantly (P<0.05) in group II and III compared to the control on day 14th of the study (Table VI).

DISCUSSION

Serum biochemical index of animals can reflect the metabolism and health status to a certain extent. Huang et al. (2017) study showed that serum Ca2+ and P3+ levels were significantly reduced after 10 days of age and were raised at 5℃ lower than the control for 3 days. Hangalapura et al. (2006) also found that cold stress significantly increased serum T3 and T4 levels of broilers. Serum AST and ALT activities increased significantly in chickens exposed to chronic cold stress (Zhang et al., 2014). Zhen et al. (2011) showed that the levels of serum CK and LDH of 4-months-old female quails were significantly increased after being exposed to cold stress for 4 h on daily basis. Different degrees of cold stress had different effects on the serum biochemical index of chickens.

With the increasing demand for animal protein, broiler farms are also increasing in many countries of the world. In the early stage, broilers are vulnerable to cold stress. Cold stress causes serious problems to chicks, ranging from reduced growth performance to high mortality. Poultry researchers have reported improvement in reducing cold stress through strengthening management improving environmental facilities and supplementation of feed additives (Su et al., 2018). Feed additives such as minerals (Yang et al., 2019; Medeiros-Ventura et al., 2020), probiotics (Huff et al., 2015; Su et al., 2018), and vitamins (Ozkan et al., 2007; Ferreira et al., 2015) to the diet can relieve cold stress in broilers. According to the results of previous studies, adding Gln to the diet of broilers can promote the growth performance and provides resistance to the cold stress (Dai et al., 2012; Hu et al., 2016).

Compared with the white phoenix chicks fed at normal temperature, when the normal feeding temperature is 5℃, the Ca2+ and P3+ in the serum decreased significantly after feeding for three days. After 15 days of experiment, the Ca2+ and P3+ in the serum did not change. When the normal feeding temperature is 10℃, three days after feeding, the serum Ca2+ content decreases significantly, and the P3+ does not change significantly. After 15 days of feeding, the serum Ca2+ content does not change significantly, and the P3+ content increases significantly (Huang et al., 2017). From the present study, it can be seen that cold stress can alter the broiler serum ions. The results of this study show that adding Gln to the diet of chicks tends to increase the serum Ca2+ content and significantly reduce serum K+, P3+ in 14-day-old chicks. The results of this study are similar to those of Zhang et al. (2018). Gln can maintain the serum ion balance of stress broilers and alleviate the harm caused by cold stress to broilers.

According to the results of previous studies, from the perspective of serum enzyme activity, cold stress has adverse effects on broilers, which may cause liver damage to broilers. The results of this experiment show that adding 1.0% ~ 2.0% Gln to the diet of chicks can reduce the serum LDH, CK, and ALT activity of chicks. This experiment is similar to the results of the Hu et al. (2016). Gln can reduce the serum LDH and CK activity, and relieve the damage caused by stress to the body.

T3 and T4 hormones play an important role in the growth and development of the body. They can promote the metabolism of proteins, sugars, and fats, thus promoting the growth and development of the body. Xiao et al. (2019) showed that dietary supplementation with different concentrations of Gln significantly increased ADFI and ADG, reduced FCR, and improved immune organ index in chicks of different ages. A certain increase in T3 and T4 levels in serum can relieve the damage caused by cold stress to the body. The results of this experiment show that supplementation of 1.0% ~ 2.0% Gln can improve T3 and T4 levels in the serum of chicks. The results of this study are similar to those of Dai et al. (2012) and Hu et al. (2016). Gln can improve T3 and T4 levels in the serum of stress broilers and mitigate the adverse effects of stress on broilers.

Supplementation with 1.5% Gln was added to the diet of chicks, and the serum albumin and globulin content of 7 days old chicks increased by 10.49 and 9.51%, respectively. Gln can improve the serum albumin and globulin levels of stressed animals, which may be due to the addition of exogenous Gln, which enhances the synthesis efficiency of proteins in animals (Zhang et al., 2015). The results of this study also show that 2.0% Gln is added to the diet of chicks, and the serum albumin and globulin content of 14-days-old chicks are significantly reduced. This may be that the high doses of exogenous Gln are added to provide nutrients, and then the deposition of albumin and globulin in the serum are accelerated into body proteins, and the potential mechanism needs to be further studied.

The increase in serum glucose content is due to the increase in glycogen decomposition in broilers at low temperatures (Zhang et al., 2014), which also indicates that animal bodies need to consume more sugar to convert into heat energy in cold environments to resist cold environments (Van et al., 2010). Summarizing the results of previous studies, it can be concluded that cold stress can increase the serum glucose, triglyceride, and uric acid content of broilers. The results of this study show that add Gln to the diet, and the serum glucose content of 7-day-old chicks decreased to varying degrees, and the serum glucose content decreased significantly. Adding exogenous Gln to cold stress chicks can provide energy for the body as an energy substance. The serum glucose content of chicks in the Gln group decreased. Add 1.0% ~ 2.0% Gln to the chick’s diet, and the serum triglyceride and uric acid content of chicks decreased to varying degrees.

In the chick stage (1 to 14-days old), too low temperature does have negative impact on serum biochemical indicators. Under this experimental condition, supplementation with Gln improves the serum biochemical indexes of cold stress chicks. Among them, adding 1.0 % Gln is the best dosage.

Acknowledgements

The authors would like to thank Dr. Qiufen Li and Dr Chenxi Deng for their assistance with the experimental analysis and the writing of this manuscript.

Funding

This study was financially supported by the National Natural Science Foundation of China (32160799), the Key R & D program of Jiangxi Province (20203BBF63021) and Jiangxi Provincial Natural Science Foundation (20224ACB205010).

Ethical approval

The project was approved by the Laboratory Animal Ethics Committee of Jiangxi Agriculture University (Nanchang, Jiangxi, China).

Statement of conflict of interest

The authors have declared no conflict of interest.

REFERENCES

Dai, S.F., Gao, F., Xu, X.L., Zhang, W.H., Song, S.X. and Zhou, G.H., 2012. Effects of dietary glutamine and gamma-aminobutyric acid on meat colour, pH, composition, and water-holding characteristic in broilers under cyclic heat stress. Br. Poult. Sci., 53: 471–481. https://doi.org/10.1080/00071668.2012.719148

Ferreira, I.B., Matos, J.B., Sgavioli, S., Vicentini, T.I., Morita, V.S. and Boleli, I.C., 2015. Vitamin C prevents the effects of high rearing temperatures on the quality of broiler thigh meat. Poult. Sci., 94: 841–851. https://doi.org/10.3382/ps/pev058

Hangalapura, B.N., Kaiser, M.G., van Poel, J.J., Parmentier, H.K. and Lamont, S.J., 2006. Cold stress equally enhances in vivo pro-inflammatory cytokine gene expression in chicken lines divergently selected for antibody responses. Dev. Comp. Immunol., 30: 503–511. https://doi.org/10.1016/j.dci.2005.07.001

Hu, H., Bai, X., Shah, A.A., Wen, A.Y., Hua, J.L., Chen, C.Y., He, S.J., Jiang, J.P., Cai, Z.H. and Dai, S.F., 2016. Dietary supplementation with glutamine and γ-aminobutyric acid improves growth performance and serum parameters in 22- to 35-day-old broilers exposed to hot environment. J. Anim. Physiol. Anim. Nutr., 100: 361–370. https://doi.org/10.1111/jpn.12346

Hu, T., Lei, Y., Li, M., Liu, Q., Song, L. and Zhao, D., 2021. Dietary Eucommia ulmoides extract alleviates the effect of cold stress on chick growth performance, antioxidant and immune ability. Animals, 11: 3008. https://doi.org/10.3390/ani11113008

Huang, L.B., Li, S.W. and Sun, M.W., 2017. Effect of cold stress of different intensity on serum biochemical indexes of white phoenix chicks. J. Tianjin Agric. Coll., 24: 59-63.

Huff, G.R., Huff, W.E., Rath, N.C., El-Gohary, F.A., Zhou, Z.Y. and Shini, S., 2015. Efficacy of a novel prebiotic and a commercial probiotic in reducing mortality and production losses due to cold stress and Escherichia coli challenge of broiler chicks. Poult. Sci., 94: 918–926. https://doi.org/10.3382/ps/pev068

Kamanli, S., Durmuş, I., Yalçın, S., Yıldırım, U. and Meral, Ö., 2015. Effect of prenatal temperature conditioning of laying hen embryos: Hatching, live performance and response to heat and cold stress during laying period. J. Therm. Biol., 51: 96–104. https://doi.org/10.1016/j.jtherbio.2015.04.001

Medeiros-Ventura, W., Rabello, C., Barros, M.R., Junior, R.S., Oliveira, H.B., Faria, A.G., Silva, A.F., Soares, P.C., Pereira, C.G., Santos, M.J.B. and Fireman, A.K., 2020. Zinc, manganese, and copper amino acid complexes improve performance and bone characteristics of layer-type chicks under thermoneutral and cold stress conditions. Poult. Sci., 99: 5718–5727. https://doi.org/10.1016/j.psj.2020.07.022

National Research Council, 1994. Nutrient requirements of poultry, 9th rev. Natl. Acad. Press, Washtington, DC.

Ozkan, S., Malayoğlu, H.B., Yalçin, S., Karadaş, F., Koçtürk, S., Cabuk, M.E.T.İ.N., Oktay, G., Özdemir, S., Özdemir, E. and Ergül, M., 2007. Dietary vitamin E (alpha-tocopherol acetate) and selenium supplementation from different sources: Performance, ascites-related variables and antioxidant status in broilers reared at low and optimum temperatures. Br. Poult. Sci., 48: 580–593. https://doi.org/10.1080/00071660701593951

Su, Y., Zhang, X., Xin, H., Li, S., Li, J., Zhang, R., Li, X., Li, J. and Bao, J., 2018. Effects of prior cold stimulation on inflammatory and immune regulation in ileum of cold-stressed broilers. Poult. Sci., 97: 4228–4237. https://doi.org/10.3382/ps/pey308

Szabó, J. andrásofszky, E., Tuboly, T., Bersényi, A., Weisz, A., Hetényi, N. and Hullár, I., 2014. Effect of arginine or glutamine supplementation on production, organ weights, interferon gamma, interleukin 6 and antibody titre of broilers. Acta Vet. Hung., 62: 348–361. https://doi.org/10.1556/avet.2014.017

van den Brand, H., Molenaar, R., van der Star, I. and Meijerhof, R., 2010. Early feeding affects resistance against cold exposure in young broiler chickens. Poult Sci., 89: 716-720. https://doi.org/10.3382/ps.2009-00432

Wang, J.T. and Xu, S.W., 2008. Effects of cold stress on the messenger ribonucleic acid levels of corticotrophin-releasing hormone and thyrotropin-releasing hormone in hypothalami of broilers. Poult. Sci., 87: 973–978. https://doi.org/10.3382/ps.2007-00281

Xiao, S.S., Ye, M.L. and Li, J.Q., 2019. Effects of glutamine on growth performance and immune organ index of cold-stressed chicks. J. Anhui Sci. Technol. Univ., 4: 9-12.

Yang, J., Zhang, M. and Zhou, Y., 2019. Effects of selenium-enriched Bacillus sp. compounds on growth performance, antioxidant status, and lipid parameters breast meat quality of Chinese Huainan partridge chicks in winter cold stress. Lipids Hlth. Dis., 18: 63. https://doi.org/10.1186/s12944-019-1015-6

Yi, G.F., Allee, G.L., Knight, C.D. and Dibner, J.J., 2005. Impact of glutamine and Oasis hatchling supplement on growth performance, small intestinal morphology, and immune response of broilers vaccinated and challenged with Eimeria maxima. Poult. Sci., 84: 283–293. https://doi.org/10.1093/ps/84.2.283

Zhang, B., Yu, C., Lin, M., Fu, Y., Zhang, L., Meng, M., Xing, S., Li, J., Sun, H., Gao, F. and Zhou, G., 2015. Regulation of skeletal muscle protein synthetic and degradative signaling by alanyl-glutamine in piglets challenged with Escherichia coli lipopolysaccharide. Nutrition (Burbank, Los Angeles County, Calif). 31: 749–756. https://doi.org/10.1016/j.nut.2014.11.010

Zhang, D., Hu, H. and Li, J.Q., 2018. Effect of glutamine on serum minerals and hormones in broilers with acute thermal stress. J. Anhui Sci. Technol. Univ., 6: 7-11.

Zhang, S.S., Su, H.G., Ying, Z.H.O.U., Li, X.M., Feng, J.H. and Zhang, M.H., 2016. Effects of sustained cold and heat stress on energy intake, growth and mitochondrial function of broiler chickens. J. Integ. Agric., 10: 2336-2342. https://doi.org/10.1016/S2095-3119(15)61314-4

Zhang, Z.W., Bi, M.Y., Yao, H.D., Fu, J., Li, S. and Xu, S.W., 2014. Effect of cold stress on expression of AMPKalpha-PPARalpha pathway and inflammation genes. Avian Dis., 58: 415–426. https://doi.org/10.1637/10763-010814-Reg.1

Zhen, L., Chen, Y. and Ji, H., 2011. Changes of some physiological indexes and serum enzyme activities in cold stressed quails. Heilongjiang Anim. Sci. Vet. Med., 5: 139-141.

Zulkifli, I.M., Shakeri, M. and Soleimani, A.F., 2016. Dietary supplementation of L-glutamine and L-glutamate in broiler chicks subjected to delayed placement. Poult. Sci., 95: 2757–2763. https://doi.org/10.3382/ps/pew267