Effects Of Gamma-aminobutyric Acid On Laying Performance And Heat Stress Resistance Capability In Hens Under High Temperature In Summer

This study was designed to investigate the effects of y-aminobutyric acid (GABA) on laying performance, egg quality and heat stress resistance capability in hens under high temperature in summer. And to apporach the mechanism from serum biochemical indexes, antioxidation, immunity and endocrine.480 Roman laying hens of 320 days of age were randomly divided into five groups with three replicates of 32 layers. One group received the basal diet as a control while the others received diets supplemented with 25,50,75,100 mg/kg GABA as treatment groups. The experiment lasted for 60 days. At 20,40,60 d of the experiment, we collected 18 eggs randomly from each group (6 eggs each repletion) to test the egg quality. At the end of the experiment,45 laying hens were slaughtered, and samples were collected for analysis.The results showed as following:(1) Production performance:production performance of laying hens was improved in all treatments, and 50 mg/kg was the best dosage which significantly increased Laying rate, average egg weight by 3.20%(P<0.05) and 3.51%(P<0.05), decreased feed weight/egg weight by 4.78%(P＜0.05). Laying rate of 25,75,100 mg/kg groups were significantly increased by 2.59%(P＜0.05),1.14%(P<0.05), 1.35%(P＜0.05), respectively. Average egg weight of 25,75,100 mg/kg groups were increased by 2.09%(P＜0.05),1.74%(P<0.05),1.51%(P>0.05) respectively. ADFI of 50,75 mg/kg groups was increased by 2.59%(P>0.05),1.46%(P>0.05), ADFI of 100 mg/kg group was decreased by 1.84%(P>0.05), and 25 mg/kg group had no difference on ADFI compared with control group.(2) Egg quality and nutrient ingredient:compared with control group,50 mg/kg GABA increased the eggshell strength, Egg shell thickness, albumen height and Haugh unit by 14.59%(P＜0.05),5.26%(P>0.05),5.37%(P>0.05),4.55% (P>0.05), respectively. The other treatment groups also improved shell thickness, yolk color and Haugh unit (P>0.05). Cholesterin of egg yolk in all the treatment groups were decreased by 5.93%(P>0.05),9.20%(P>0.05),7.65%(P>0.05), 7.24%(P>0.05), respectively. There were no significant differences on water percentage, yolk weight proportion, albumen weight proportion and yolk fat percentage between all the groups. Amino acid of egg:the total amino acid of albumen or yolk in all treatment groups were increased (P>0.05), and 50mg/kg GABA increased the total amino acid of albumen and yolk by 2.49%(P>0.05), 2.57%(P>0.05), respectively. Glutamic acid of egg albumen was increased by 3.12%(P>0.05),5.48%(P>0.05),4.18%(P>0.05),3.19%(P>0.05), respectively in treatment groups. Glutamic acid of egg yolk was increased by 3.73%(P>0.05), 5.72%(P>0.05),4.48%(P>0.05),4.23%(P>0.05), respectively in treatment groups. Tyrosine acid in egg albumen was increased by 1.98%(P>0.05),5.25% (P>0.05),4.92%(P>0.05),3.28%(P>0.05), respectively in treatment groups. Tyrosine acid in egg yolk was increased by 3.48%(P>0.05),5.22%(P>0.05), 4.35%(P>0.05),3.48%(P>0.05), respectively in treatment groups.(3) Serum biochemical indexes:compared with control group,4 treatment groups increased content of Ca by 3.42%(P>0.05),12.84%(P>0.05),10.78%(P>0.05), 0.51%(P>0.05), respectively. Increased the serum P by 22.03%(P<0.05),26.27% (P<0.05),25.00%(P<0.05),10.59%(P>0.05), respectively. Increased the serum GLU by 16.52%(P>0.05),30.70%(P<0.05),13.51%(P>0.05),5.96%(P>0.05), respectively. And decreased BUN by 7.69%(P>0.05),13.00%(P>0.05),4.77% (P>0.05),4.77%(P>0.05), respectively. Decreased CHO by 8.41%(P＜0.05), 20.21%(P＜0.05),19.49%(P＜0.05),9.75%(P>0.05), respectively. Increased the total protein by 9.63%(P>0.05),11.43%(P＜0.05),1.98%(P>0.05),4.32% (P>0.05), respectively. And increased the serum albumen by 4.67%(P>0.05), 13.59%(P>0.05),0.63%(P>0.05),0.86%(P>0.05), respectively.50 mg/kg GABA decreased the GOT and GPT levels by 6.81%(P＜0.05),7.24%(P>0.05), respectively, decreased LDH (lactate dehydrogenase) by 8.42%(P>0.05). And the serum enzyme activity had no obvious difference between the others treatment groups.(4) Antioxidation parameters:compared with control group,4 treatment groups increased the serum GSH-Px activity by 8.1%(P<0.05),10.71%(P＜0.05),1.17% (P>0.05),0.50%(P>0.05), respectively. The serum SOD activity were increased by 3.14% (P>0.05),5.94% (P＜0.05),4.45%(P>0.05),2.39% (P>0.05), respectively. The serum MDA content were significantly decreased by 31.05% (P＜0.05),44.55%(P＜0.05),40.59%(P＜0.05),35.91%(P<0.05), respectively. The enzymes activity of liver was also increased.50 mg/kg GABA increased the GSH-Px and SOD activity in liver by 9.45(P＜0.05),4.09%(P＜0.05), respectively, and decreased the content of MDA in liver by 11.14%(P>0.05).(5) Immune parameters:compared with control group,50 mg/kg GABA increased the levels of IgG, IgA, complement 3 by 22.88%(P＜0.05),21.99%(P＜0.05),26.31% (P＜0.05), respectively. The other treatment groups had no significant effect on levels of IgG, IgA, and complement 3. Immune Organ Index, IgM, complemente C4 had no significant difference among all the groups.(6) Endocrine hormones:compared with control group,50 mg/kg GABA significantly increased the concentration of FSH, E2 by 18.67%(P＜0.05),13.03%(P＜0.05) respectively, decreased the concentration of PRL by 11.56%(P>0.05). The level of serum insulin, T3 and FT3 was significantly increased by 69.67%(P＜0.05), 23.78%(P＜0.05),19.01%(P＜0.05), respectively in 50 mg/kg group.(7) Digestive enzymes activity:compared with control group,25,50,75,100 mg/kg GABA increased the amylase activity by 2.84%(P>0.05),9.78%(P>0.05),4.10% (P>0.05),2.84%(P>0.05), respectively. And increased the lipase activity by 1.28%(P>0.05),9.08%(P>0.05),9.22%(P>0.05),3.43%(P>0.05), respectively. 50,75, 100mg/kg GABA increased parenzyme activity by 7.87%(P>0.05),4.28% (P>0.05),3.40%(P>0.05), respectively. And 25 mg/kg GABA had no obvious effect on parenzyme activity.The result indicated that:①supplement with GABA in diet could effectively improve the production performance and egg quality of laying hens during high temperature in summer, and 50mg/kg was the best dosage.②GABA could facilitate the secretion of FSH and E2, and inhibit the secretion of PRL. GABA could enhance the secretion of thyroid gland, maintain the stability of endocrine system and alleviate heat stress, to increase the laying rate.③GABA could increase total protein levels; enhance the capacity of protein synthesis of laying hens. It could increase the level of GLU, serum Ca and P.④GABA could enhance the antioxidant capacity by increasing the activity of antioxidant enzymes in liver and strengthen immune function by increasing the concentration of serum immunoglobulin and complement. So it can alleviate the heat stress.