Effects Of Sustained Release Of Synthetic Amino Acids On Efficient Utilization Of Low Protein Diet And Intestinal Barrier Function Of Laying Hens

At present,the main problems facing livestock production are the shortage of protein feed resources and the large emission of nitrogen and phosphorus pollutants in large-scale production.The application of low protein diet technology can alleviate the above problems to some extent.However,production performance may be reduced by the use of low protein diets in laying hens.The aim of this study was to analyse the effects and mechanisms of low protein diets on the performance of laying hens and to investigate the effects of low protein diets based on the sustained release of synthetic amino acids on the performance,intestinal barrier function and nitrogen excretion of laying hens in order to provide evidence for the efficient use of low protein diets in laying hens.Experiment 1 Effects of low protein diet on performance and intestinal barrier function of laying hens.A total of 270,32-week Hyline brown laying hens with similar laying rate were randomly divided into 2 treatments,the crude protein levels of the control group（CON）and experimental group（LCP）were 16%and 14%.The supplementation of essential amino acids with crystal amino acids in the LCP group was consistent with that in the CON group.The supplementation of essential amino acids with crystal amino acids in the LCP group was consistent with that in the CON group.The experiment lasted for 8 weeks,and the production performance was measured weekly.At the end of the experiment,blood and intestinal mucosal samples were collected and blood biochemistry and intestinal barrier function indexes were determined.The results showed that compared with CON group,egg weight in LCP group had a tendency to decrease（P=0.08）;LCP group significantly decreased the m RNA expression levels of Claudin,Occludin in duodenum and jejunum,Claudin and Occludin in ileum（P<0.05）,the m RNA expression levels of b^0,+AT,r BAT,B⁰AT and Pep T1in jejunum of LCP group were significantly decreased（P<0.05）.Experiment 2 Effects of different forms of amino acid supplementation on performance and intestinal barrier function of growing laying hens under low protein diet.A total of 288,9-week Hyline brown laying hens with similar body weight were randomly divided into 3treatments,The crude protein level of the control group（CON）was 15.5%,and the crude protein level of the crystal amino acid supplement group（LCP-CAA）and the coated amino acid group（LCP-MAA）was 12.5%.The amino acid level of the crystal and coated amino acid supplement groups was consistent with that of the CON group.The duration of the experiment was 8 weeks,with production performance measurements every week and body measurements every two weeks.Blood and intestinal mucosal samples were collected at week4 and 8.At the end of the experiment,digestion and metabolism tests and amino acid metabolism tests were carried out respectively.The results showed that there were no significant differences in body weight,daily gain and feed intake among all treatments（P>0.05）;At 4 h after feeding,Ile,Val and His in LCP-MAA group were significantly lower than those in CON group（P<0.05）,At 6 h after feeding,Thr,Arg,TEAA and TAA in LCP-MAA group were significantly higher than those in CON group（P<0.05）;Compared with CON group,DAO and D-LA activity in blood in LCP-MAA group were significantly decreased（P<0.05）;Compared with the LCP-MAA group,the ratio of villus height to crypt depth in the LCP-MAA group tended to increase（P=0.07）;LCP-MAA group significantly increased the m RNA expression level of MUC-2 in duodenum and Occludin in jejunum（P<0.05）,the m RNA expression levels of y⁺LAT1 and b⁰⁺AT in jejunum and ileum in LCP-CAA group were significantly increased at 8 wk（P<0.05）;The fecal nitrogen content of low protein diet group was significantly decreased（P<0.01）,and the average daily nitrogen release was decreased by more than 10%.Experiment 3 Effects of different forms of amino acid supplementation on performance and intestinal barrier function of laying hens under low protein diet.The experiment lasted for12 weeks,and the production performance was counted weekly.At the 6 and 12 week,blood and intestinal samples were collected.At the end of the experiment,digestion and metabolism tests and amino acid metabolism tests were carried out respectively.The results showed that the FCR and ADFI of LCP-CAA group were significantly higher than those of CON and LCP-MAA（P<0.05）,but there were no significant differences in laying rate,egg weight and egg mass among all groups（P>0.05）;At 2 h after feeding,His in LCP-CAA group was significantly higher than that in LCP-MAA group（P<0.05）,At 4 h after feeding,the contents of Met,Thr,Leu and Val in blood of LCP-MAA group were significantly increased（P<0.05）,At 6 h after feeding,Trp,Ile and Arg in LCP-MAA group were significantly increased（P<0.05）;Compared with the LCP-CAA group,the blood D-LA activity in the LCP-MAA group tended to decrease（P=0.08）;The contents of chylase in duodenum in LCP-CAA group were significantly decreased（P<0.05）,and the contents of chylase and trypsin in ileum in LCP-MAA group were significantly increased（P<0.05）;In LCP-MAA group,m RNA expression levels of Occludin,ZO-1 in duodenum and Occludin,ZO-1,y⁺LAT1 in jejunum and ZO-1 in ileum significantly increased at 8wk and 12wk（P<0.05）;Fecal nitrogen content in low protein diet group was significantly decreased（P<0.01）,The average daily nitrogen emission of LCP-CAA and LCP-MAA was respectively decreased by 13.1%and 20.5%.In conclusion,under the crystal amino acid supplement mode,the reduction of dietary crude protein level by more than 2%affects the performance of laying hens,and supplementation of coated amino acids can significantly improve the performance decline.The mechanism is related to the balanced absorption and utilization of digested amino acids of laying hens.Under the conditions of this experiment,reducing dietary crude protein level and supplementing crystalline amino acids can improve intestinal barrier function,promote digestive enzyme secretion,increase the expression of amino acid transporters,improve dietary protein utilization efficiency,and reduce nitrogen emission of laying hens to some extent.