Effects Of Different Levels Of Ellagic Acid On Growth Performance And Meat Quality Of White-Feathered Broilers Under Heat Stress

As a kind of plant polyphenols,Ellagic acid（EA）has many physiological functions such as antioxidant,anti-inflammatory,lipid metabolism regulation and anticancer.Heat stress caused by high temperature is a common problem in livestock and poultry production.In order to reduce the loss caused by heat stress to animal production,it is particularly important to find effective green additives to alleviate heat stress.To study the effects of ellagic acid on growth performance and meat quality of white-feathered broilers under heat stress,four hundred one-day-old Arbor Acres broilers（AA broilers）were fed a basal diet.A total of 300 healthy broilers with similar body weight at 14 days of age were randomly divided into 5 groups with 6 replicates per group and 10 broilers per replicate.Piglets in control group were fed a basal diet,and those in experimental groups were fed the basal diet supplemented with 0.075,0.15,0.3 and 0.6 g/kg ellagic acid,respectively.Heat stress treatment began at 14 days of age and ended at 42 days of age,and the experiment lasted for28 days.Samples were collected at the 28th and 42nd days of the experiment,respectively,to investigate the effects of ellagic acid on heat stress indices,growth performance,slaughter performance,meat quality,conventional muscle nutrients,antioxidant performance,free radical scavenging ability and gene expression of white-feathered broilers under heat stress.The results showed that:（1）Compared with the control group,0.15 g/kg and 0.6 g/kg ellagic acid supplementation significantly reduced serum corticosterone（CORT）level at 28d and 42d（P<0.05）.The CORT content of 28d and 42d showed a quadratic curve with dietary ellagic acid supplemental level increasing（P<0.05）,according to the regression equation calculation,when dietary ellagic acid supplemental level is 0.277-0.288 g/kg,it has the best effect on alleviating heat stress inhibition of broilers.（2）Compared with the control group,the supplementation of 0.3 mg/kg ellagic acid significantly decreased the average daily gain（ADG）during 14-28 days（P<0.05）,and significantly increased the feed/gain（F/G）（P<0.05）;The supplementation of 0.075 g/kg and0.15 g/kg ellagic acid significantly increased the final body weight in 42d（P<0.01）.The final weight of 42d showed a quadratic curve with the increase of dietary ellagic acid supplemental level（P<0.05）,according to the regression equation calculation,when dietary ellagic acid supplemental level is 0.182 g/kg,the growth performance of broilers under heat stress is the best.（3）Compared with the control group,ellagic acid supplementation with 0.15 g/kg significantly decreased serum alanine aminotransferase（ALT）level（P<0.05）and increased serum glucose（GLU）level（P<0.05）.There was no quadratic relationship between serum biochemical indices and dietary ellagic acid supplemental level（P>0.05）.（4）Compared with the control group,adding 0.15 g/kg ellagic acid significantly increased the breast muscle percentage（P<0.05）.There was no quadratic relationship between slaughter performance index and dietary ellagic acid supplemental level（P>0.05）.（5）Compared with the control group,different doses of ellagic acid could significantly increase the p H_24h and△p H of breast muscle（P<0.01）,and significantly decrease the 24h drip loss of breast muscle（P<0.05）.The addition of ellagic acid could significantly increase the△p H of thigh muscle（P<0.01）,and the addition of 0.3 g/kg ellagic acid could significantly increase the p H_24h of thigh muscle（P<0.05）.In terms of meat color,ellagic acid supplementation increased the redness a^*of breast muscle and thigh muscle,but decreased the brightness L^*and yellowness b^*,but there was no significant difference（P>0.05）.The p H_24h（P<0.001）、△p H（P=0.001）、24h drip loss（P<0.05）of breast muscle and△p H of thigh muscle（P<0.001）showed a quadratic curve with the increase of dietary ellagic acid supplemental level,and the regression equation calculated that when dietary ellagic acid supplemental level was 0.333-0.366 g/kg,the meat quality of broilers under heat stress was the best.（6）Compared with the control group,adding 0.15 g/kg ellagic acid significantly increased the crude protein content under fresh weight of thigh muscle（P<0.05）.There was no quadratic relationship between routine muscle nutrient and dietary ellagic acid supplemental level（P>0.05）.（7）Compared with the control group,ellagic acid supplementation significantly increased the total antioxidant capacity（T-AOC）,the activities of superoxide dismutase（SOD）,catalase（CAT）,glutathione peroxidase（GSH-Px）（P<0.01）,and significantly decreased the activity of malondialdehyde（MDA）in breast muscle（P<0.01）.The T-AOC,SOD and CAT activities of thigh muscle were significantly increased（P<0.01）,while MDA activity was significantly decreased（P<0.01）.The T-AOC（P=0.001）、SOD（P<0.05）、CAT（P<0.05）、GSH-Px（P<0.05）、MDA（P<0.01）of breast muscle and T-AOC（P<0.05）、SOD（P<0.05）、CAT（P<0.05）of thigh muscle showed a quadratic change with dietary ellagic acid supplemental level increasing,and the regression equation calculated that when dietary ellagic acid supplemental level was 0.284-0.321 g/kg,the antioxidant capacity of broilers under heat stress was the best.（8）Compared with the control group,ellagic acid supplementation significantly increased the free radical scavenging ability of breast muscle and thigh muscle（P<0.05）.The contents of 2,2-biazo-bis（3-ethyl-benzothiazol-6-sulfonate）diammonium salt（ABTS⁺）,protein carbonyl（PC）,hydroxyl radical（OH^-）and superoxide anion（O₂^-）in breast muscle were significantly decreased（P<0.01）.ABTS⁺and PC contents in thigh muscle were significantly decreased（P<0.05）,and OH^-content was extremely significantly decreased（P<0.01）.ABTS⁺、OH^-、O₂^-in breast muscle and OH^-in thigh muscle showed a quadratic curve with dietary ellagic acid supplemental level increasing（P<0.05）,according to the regression equation calculation,when dietary ellagic acid supplemental level is 0.293-0.335g/kg,the free radical scavenging ability of broilers under heat stress is the best.（9）Compared with the control group,ellagic acid supplementation significantly increased the gene expression levels of GSH-Px（P<0.01）,CAT（P<0.05）,nuclear factor erythrocyte 2 related factor（Nrf2）（P<0.05）in breast muscle,decreased the gene expression levels of heat shock protein 70（HSP70）（P<0.05）and heat shock protein 90（HSP90）（P<0.01）.Compared with the control group,ellagic acid supplementation significantly increased GSH-Px and Nrf2 gene expression levels in thigh muscle（P<0.01）,and significantly decreased HSP90 gene expression levels in thigh muscle（P<0.05）.The m RNA expression levels of GSH-Px、CAT、Keap1、Nrf2、H70、H90 in breast muscle and GSH-Px、Nr F2、H90 in thigh muscle showed a quadratic curve with dietary ellagic acid supplemental level increasing（P<0.05）.By regression equation calculation,The range was optimized with the corticosterone level and performance as the decisive factors,and the supplemental level of 0.182-0.288 g/kg ellagic acid could alleviate the heat stress effect and improve the performance of white-feathered broilers.Taking meat quality as the decisive factor to optimize the interval,the supplementation level of 0.333-0.352 g/kg ellagic acid could best improve the meat quality of heat-stressed white-feathered broilers.In conclusion,dietary ellagic acid supplementation can improve the growth performance,meat quality,antioxidant performance and antioxidant gene expression of white-feathered broilers under heat stress,and reduce the overexpression of HSP70 and HSP90.Under the experimental conditions.Under the experimental conditions,the optimal supplemental level of ellagic acid in the diet of heat-stressed white broilers is 0.182-0.377g/kg.