Effects Of Weaning Stress On The Structural And Functional Development Of Digestive Tract Of Lamb And Its Mechanism

Indoor feeding and large-scale intensive feeding have become the main trend of of China's meat sheep industry,but which significantly increased the feeding costs.The key to improve the production efficiency of indoor feeding in rural areas is to increase the reproductive rate of ewes and shorten the breeding cycle.This requires the application of early weaning technique.However,weaning stress may have a multi-faceted effect on the physiology of the lamb and affect the structure and function development of the digestive tract.Based on the analysis of the growth performance,systemic immunity and stress related indicators of lambs and the dynamic changes of nutrient digestion,this experiment further studied the effects of weaning on rumen and intestinal tissue morphology,fermentation function,digestive enzyme activity,antioxidant index and immune index.The short-term effects and long-term effects of weaning on the structure and function of the digestive tract of lambs were evaluated.Combined with rumen and intestinal microbial diversity analysis and transcriptome analysis,the main mechanisms of weaning stress affecting the structure and function of digestive tract in lambs were discussed.1 Effects of weaning on growth performance,immunity related indicators and nutrient digestion in lambsTwelve pairs of whole sibling newborn lambs were selected,and each pair of sibling lambs was randomly assigned to the control group?CON,birth weight = 3.35 ± 0.76 kg,n = 12?and the weaning group?EW,birth weight = 3.26 ± 0.62 kg,n = 12?.The growth performance,plasma immunity and stress related indexes and nutrient digestion dynamics of lambs were determined.The results showed that although weaning increased feed intake,it significantly reduced lamb growth performance.Early weaning affects HPA axis hormone levels and blood immune indicators 1-3d after weaning,but the duration is very short,and will gradually recover after 7d.However,weaning has a continuous effect on nutrient digestion,reducing the feed intake of DM,CP,EE,digestibility per kg body weight and digestibility,but increasing the feed intake of starch,NDF and ADF and digestibility.2 Effects of weaning on rumen tissue morphology and function in lambsThis experiment evaluated the short-term?26 days old,5 days after weaning?and long-term?49 days old,5 days after weaning?effects of weaning on rumen tissue morphology,rumen fluid volatile fatty acids,nitrogen metabolism index,enzyme activity,rumen tissue pH regulation,VFA metabolism and rumen development related gene expression.The results showed that the short-term effects of weaning on rumen structure and function development were limited and long-term effects were significant.Weaning increased rumen weight,but decreased nipple width and muscle thickness,and decreased rumen VFA concentration and nitrogen concentration.Weaning significantly increased the expression of HMGCL mRNA in rumen tissues,significantly decreased the expression of DRA and IGFBP6 mRNA.Rumen development requires physical stimulation to promote rumen development through ketone production and ketone transport and other physiological processes.3 Effect of weaning on the rumen microflora of lambsThis experiment analyzed the effect of weaning on rumen microbial flora in lambs,and further analyzed the relationship between microflora and rumen morphology and fermentation function.Weaning and age significantly affected beta diversity.At the phylum level,the relative abundance of Fibrobacteres in the weaning group was significantly lower than that in the control group?P < 0.05?.The relative abundance of Bacteroidetes in the weaning group was significantly higher than that in the control group,and the relative abundance of Proteobacteria and Cyanobacteria.At the genus level,weaning significantly increased the relative abundance of Prevotella₁ and Prevotellaceae_UCG-001?P < 0.05?.The results of CCA analysis and VPA analysis indicate that VFA levels among all ecological factors may be key factors affecting microbial communities.The rumen microbial flora is closely related to rumen tissue morphology and fermentation function.4 Effects of weaning on intestinal morphology and function of lambsThis experiment analyzed the short-term and long-term effects of weaning on the intestinal morphology,digestive enzyme activity,antioxidant activity,immune index and apoptosis of the lamb.The results showed that weaning reduced intestinal lactase activity and increased amylase activity.Weaning caused oxidative damage of ileal cells,reduced ileal villus height,and promotes differentiation and proliferation of intestinal epithelial cells.Weaning inhibits apoptosis,which may be a regulatory mechanism for intestinal tissue to maintain the epithelial cells number under weaning stress conditions.5 Effect of weaning on the intestinal microflora of lambsThis experiment analyzed the effects of weaning on the jejunum and ileum microflora of lambs.The ? diversity index of jejunum microbial species,Chao1 index and ACE index in weaning group increased,but weaning had no effect on ileum alpha diversity index.Weaning had no significant effect on beta diversity in the jejunum and ileum.At the genus level,weaning significantly increased the relative abundance of jejunum Succinivibrio and Methanobrevibacter,significantly increasing the relative abundance of ileal Prevotella₁ and Treponema₂.6 Effects of weaning on the intestinal transcriptome of lambsIn this study,the effect of weaning on the intestinal transcriptome of lambs was studied by transcriptome sequencing technology.The number of differential expressed genes between the weaning group and the control group was very different at 49 days of age vs 26 days of age.Compared with EW49 and CON49 group,the differentially expressed genes were mainly enriched in the process of redox process,immune response,antiviral reaction,protein phosphorylation,sterol homeostasis,and cell differentiation regulation.Compared with EW26 and CON26 group,the differentially expressed genes were mainly enriched in the biological processes,such as immune response,chemotaxis,anti-oxidation process,oxidative stress response,and regulation of inflammatory response.In combination with the most significantly up-regulated or down-regulated genes and their functions,weaning promote intestinal immune responses and intestinal cells differentiation and proliferation through transcriptional regulation,but inhibit apoptosis.In summary,21 d weaning significantly reduced the growth performance of lambs.Weaning affects rumen structure and function development.Rumen development requires adequate SCFAs and physical stimulation through ketone production and ketone transport and other physiological processes.Rumen development is closely related to microflora.Weaning promotes the intestinal immune response and the cell cycle progression of the intestinal tissue through transcriptional regulation,including promoting intestinal cell differentiation,proliferation and necrosis,but inhibits the process of apoptosis,which may be the regulating mechanisms for maintaining the number of intestinal villi cells and intestinal barrier function during stressful situation.