| The purpose of this experiment was to investigate the effects of humic acids from two different sources on the laying performance,egg quality,antioxidant capacity,egg-producing hormone and intestinal morphological function of laying hens at later stage and under high temperature and heat stress conditions,so as to provide scientific basis for the application of humic acids in the actual production of laying birds.The main findings are as follows:Trial 1:Effects of humic acid in feed on laying hens at later stageFour hundred and five 52-week-old Hy-Line White laying hens with similar weight(1.31±0.12 kg)and laying rate(81.39±0.23%)were randomly divided into 3 groups with 9 replicates for each group and 15 laying hens for each replicate.The control group was fed the basic diet(CON group),the experimental group 1(HAA group)and the experimental group 2(HAB group)were fed with the basic diet+1000 mg/kg humic acid A and the basic diet+1000 mg/kg humic acid B,respectively.The trial was conducted for period of 8 weeks.The results showed that:1)compared with CON group,laying rate of laying hens fed with 1000 mg/kg HAA increased significantly(P<0.01),while the difference of HAB group was not significant(P>0.05).The average egg weight of HAA and HAB were significantly increased(P<0.05),and the F/E(P<0.01)and unqualified egg rate were decreased(P<0.05).2)compared with CON group,TG content in serum of both HAA and HAB groups was significantly reduced(P<0.01),LDH activity in serum of HAB was increased(P<0.05),and ALB content in serum of HAA group were decreased(P<0.05).3)compared with the control group,treatments in HAA and HAB had no significant effect on on serum FSH(P>0.05).HAs significantly increased the content of LH in serum(P<0.01),and the effect of HAA group was more significant than that of HAB group(P<0.01).4)compared with the control group and HAA group,the addition of 1000 mg/kg HAB diet significantly increased the GSH-Px activity in the liver of laying hens(P<0.05).Trial 2:Effects of humic acid in feed on laying hens under heat stressBased on trial 1,the effect of humic acid on laying hens under heat stress was further explored.450 feathers 60-week-old laying hens with similar weight(1.23±0.25kg)and laying rate(80.45±0.16%)were randomly divided into control group 1(CON1 group),control group 2(CON2 group),experimental group 1(HAA group)and experimental group 2(HAB group).CON1 group was fed with the basal diet at room temperature(25±1℃);CON2 group was fed with the base diet at high temperature(35±1℃);HAA group was fed with the basic diet supplemented with 1000 mg/kg humic acid A at high temperature;HAB group was fed with the base diet supplemented with 1000 mg/kg humic acid B at high temperature.There were 9 replicates per group and 15 laying hens per replicate.And this trial was conducted for 4 weeks.Results showed that:1)compared with CON1 group,laying rate and ADFI of laying hens in three heat stress groups(CON2,HAA and HAB groups)were significantly decreased(P<0.01)and unqualified egg rate was significantly increased(P<0.01).However,compared with CON2 group,laying rate of HAA group was significantly increased(P<0.01)and unqualified egg rate was significantly decreased(P<0.01),while there is no significant difference in HAB group(P>0.05).2)compared with CON1 group,heat stress made a significant reduction of Haugh unit in CON2 group(P<0.05).Compared with CON2 group,HAA and HAB group significantly improved Haugh unit of eggs significantly(P<0.05).3)compared with CON1 group,heat stress significantly reduced the content of total protein(P<0.05)and increased the content of uric acid,and the enzyme activity of alkaline phosphatase,lactate dehydrogenase,creatine kinase and alanine aminotransferase activity(P<0.01)of serum in CON2 group.Compared with CON2 group,the content of the total protein in serum of HAA and HAB groups was significantly increased(P<0.05),and the content of uric acid and the activity of alkaline phosphatase,lactate dehydrogenase,creatine kinase and alanine aminotransferase were significantly decreased(P<0.01).4)Compared with CON1 group,the serum LH level in three heat stress groups was significantly decreased(P<0.01).However,compared with CON2 group,the serum LH level in HAA group was increased significantly(P<0.01).5)Compared with CON1 group,heat stress significantly increased the activity of catalase in serum and liver(P<0.05,P<0.01)and the content of malondialdehyde in liver in CON2 group(P<0.01).Compared with CON2,HAA and HAB groups significantly decreased the activity of catalase in serum(P<0.05)and the content of malondialdehyde in liver(P<0.01),and HAA group significantly decreased the activity of catalase in liver(P<0.01).6)compared with CON1 group,the villi in three groups under heat stress showed different degree of rupture,and the jejunum villi height and velvety ratio and ileal villi height in CON2,HAA and HAB groups all decreased significantly(P<0.01).However,compared with CON2 group,the height and V/C of jejunum villi in both HAA and HAB group were increased significantly(P<0.01),while the ileal villi height in HAB group was significantly increased(P<0.01).7)compared with CON1 group,heat stress significantly increased the mRNA expression of jejunum HSP70,HSP90,ZO-1 and Occludin in CON2 group(P<0.01).But compared with CON2 group,the mRNA expressions of HSP70,HSP90,ZO-1 and Occludin in HAA and HAB groups were significantly decreased(P<0.01),and the improvement effect of HAA group was better.To sum up,in this experimental conditions,the addition of 1000 mg/kg humic acid in diet can effectively enhance the oxidation resistance under the condition of normal temperature,promote the luteinizing hormone secretion and improve the laying performance at later stage.And under the condition of heat stress,the supplementation of humic acid can reduce the metabolism of the body’s endocrine disorders caused by high temperature,improve the oxidation resistance,protect the intestinal morphology and function,keeping laying hens normal laying performance.And the effect of natural humic acid,which formed naturally by humus,is better. |
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