Effects Of Rearing Patterns On Growth And Digstive Tract Development In Yak Calves

Calves are the basis of sustainable and high-quality development for yak production.A scientific feeding strategy for calf is the basis for efficient breeding of yaks,and can improve yak production efficiency.Currently,the feeding pattern of yak calves are maternal + grazing,while suckling time is about 5-6 months and the average milk production is only 1.29 kg/d.The limited nutrition of grazing can cause serious imbalance between dietary nutrient and requirement for calf growth,which will limit the quality of calf growth and development,as well as adult performance.Simultaneously,constant suckling of calves prevented the yak cows from breeding properly,reducing its reproductive performance.Therefore,on the premise of ensuring the growth and development of yak calves,it is of great significance to implement timely weaning cultivation to improve the quality and efficiency of yak industry.In this study,feeding test,slaughtering test and gene sequencing analysis were used to explore the effects of "maternal + grazing" and "replacer + supplementary feeding" rearing patterns on the growth performance and digestive tract development of yak calves.So that the molecular mechanism of replacer + supplementary feeding rearing pattern regulates the growth and rumen development of yak calves were explored,providing theoretical basis for early breeding of yak calves in plateau area.Experiment 1.Effects of rearing patterns on growth performance,organ weight and blood index of yak calvesA total of twenty healthy male yak calves(30-day-old)were divided equally into four groups: SA group(milk replacer + supplementary feeding Starter + Alfalfa hay),S group(milk replacer + supplementary feeding Starter),A group(milk replacer + supplementary feeding + Alfalfa hay)and MG group(Maternal + Grazing).During the experiment,these calves of SA,S and A groups were fed same milk replacer powder separately.Meanwhile,according to the experimental group,the calves were free to intake the starter and alfalfa,and drink freely.For MG group,these yak calves following with yak cows by feeding and grazing.The experimental period was 90 days totally.After the experiment,the body weight and body size were measured.After the blood was collected,the carcass weight and organ weight were measured.The results showed that the body weight of yak calves in SA group,S group,A group and MG group were 87.90±0.71 kg,70.70±1.45 kg,77.10±2.36 kg and 64.50±3.34 kg,and the daily gain were 562.9±16.6 g,422.5±31.4 g,482.0±8.1 g and 358.1±15.9 g respectively.Compared with MG group,SA group significantly increased the dry matter intake and carcass weight of yak calves(P<0.01),and significantly improved feed conversion efficiency(P<0.05).Meanwhile,the body weight and daily gain of replacement + supplementary groups were significantly higher than those of maternal + grazing group(P<0.01).The weight of heart,liver,spleen,lung,kidney and thymus in SA group were significantly higher than that in MG group(P<0.05).The contents of ALB,BUN,Ca and P in serum of yak calves in SA,S and A groups were significantly higher than those in MG group(P<0.05),and the contents of TP in group SA and group A were significantly higher than those in MG group(P<0.05).To sum up,compared with maternal+grazing,replacer+supplementary feeding significantly improved the dry matter intake and the intake level of nutrients,increased the weight,body size and organ weight of yak calves,and then effectively explored the potential growth performance of suckling yak calves.Experiment 2.Effects of rearing patterns on rumen fermentation,digestive enzymes and epithelial tissue development of yak calvesOn the basis of making clear that replacer+supplementary feeding can significantly improve the growth performance and organ weight development of suckling yak calves,this experiment further studies the effect of replacer+supplementary feeding rearing pattern on the rumen morphology and function development of yak calves.Collecting rumen fluid,chyme,and epithelial tissue samples from yak calves in experiment 1.The rumen fermentation,digestive enzyme activity,rumen epithelial tissue morphology,and other indexes were measured by using histomorphology observation,ELISA,real-time quantitative PCR,and transcriptome sequencing analysis.The transcriptome sequencing was carried out to analyze the rumen tissue gene expression.The results showed that the concentrations of propionate,butyrate,iso-butyrate,valerate,isovalerate and TVFA in rumen fluid of SA group and S group were significantly higher than those of MG group(P<0.05).The rumen carboxymethyl cellulase and pectinase activities in A group were significantly higher than those in MG group(P<0.01).The length of rumen papilla in SA,S and A groups was significantly higher than that in MG group(P<0.05),and the width of rumen papilla in SA and S groups was significantly higher than that in MG group(P<0.05).Compared with MG group,there were 1130 genes differentially expressed in rumen tissue of SA group,including 418 genes with high expression and 712 genes with low expression.In S group,there were 1511 differentially expressed genes,463 of which were high expression genes and 1047 of which were low expression genes.In A group,1460 genes were differentially expressed in rumen,including 516 genes with high expression and 944 genes with low expression.Compared with the maternal + grazing group,the replacer + supplementary feeding group significantly enhanced rumen fermentation capacity and digestive enzyme activity,and promoted the morphological development of rumen epithelium of yak calves.The different expression of genes related to rumen development in suckling yak calves was significantly changed by the way of replacer + supplementary feeding rearing patterns.The genes mainly involved in the biological process of rumen epithelium development,metabolism and immunity.The significant enrichment pathway of KEGG was mostly related to immune regulation,which ensured the healthy development of rumen in suckling yak calves.Experiment 3.Effects of rearing patterns on intestinal morphology,digestive enzymes and mucosal immunity of yak calvesthe early development of rumen morphology and function of yak calves was effectively promoted by supplementary feeding in the experiment 2.In this experiment,we continued to study how replacer+supplementary feeding affects the intestinal morphology and function development of lactating yak calves.To observed the intestinal morphology,digestive enzyme activity and mucosal immunity of yak calves,we collected epithelial tissues,mucosa and chyme samples from the small intestine in yak calves from experiment 1.Histomorphology and ELISA were used in this study.The results showed that the length of epithelial villi and the depth of crypt in duodenum,jejunum and ileum in SA group were significantly higher than those in MG group(P<0.01),and the length of epithelial villi and the depth of crypt in duodenum,jejunum and ileum were SA group>S group>A group(P<0.01).The activities of α-amylase in the duodenum and jejunum and trypsin in the jejunum in SA group,S group and A group were significantly higher than those in MG group(P<0.01),while,the activities of lipase in the duodenum and jejunum in MG group were significantly higher than those in SA group,S group and A group(P<0.01).The IL-1β content in duodenal mucosa,SIg A,IFN-γ,IL-1β,IL-2 and TNF-α contents in jejunal mucosa,and IFN-γ and IL-1β contents in ileal mucosa were significantly higher in SA group than those in MG group(P<0.05).To sum up,compared with the maternal+grazing,replacer+supplementary feeding rearing patterns significantly improved the morphological development of intestinal epithelium,enhanced the secretion of α-amylase and trypsin in the anterior and middle segments of the small intestine,enhancing the nutrition absorption and utilization,and immune capacity of the intestine in suckling yak calves.Experiment 4.Effect of rearing patterns on microflora composition of digestive tract in yak calvesBased on the previous three experiments,this experiment system carried out to study different rearing patterns on the composition of digestive tract microbiota of yak calves,to explore the internal mechanism of replacer + supplementary feeding rearing patterns regulating the development of digestive tract of suckling yak calves,We collected the chyme samples of the rumen,jejunum,ileum and cecum of yak calves in experiment 1 and extracted high-quality total DNA samples for 16 S r DNA high-throughput sequencing to analyze the rumen and intestinal microorganisms.The results showed that compared with the maternal + grazing group,the replacer + supplementary feeding groups significantly increased the diversity and richness of the microbial community in the digestive tract of yak calves,and increased the abundance of bacteria genus which mainly participated in the utilization of fiber and non-fiber carbohydrate including Atopobium,Clostridium＿XIVb,Acinetobacter,Oscillibacter,Dialister,Desulfovibrio,Bacteroides,Lachnospiracea＿incertae＿sedi and Clostridium＿sensu＿stricto genus in rumen.There were Odoribacter,Lachnospira,Propionibacterium,Synergistes,Atopobium,Succiniclasticum,Anaerovibrio,and Lachnospiracea＿incertae＿sedis existed in the jejunum and ileum.There were as follows Anaerovibrio,Succiniclasticum,Vulcaniibacterium,Synergistes,Eubacterium,Cellulosilyticum,Butyrivibrio,Parabacteroides,Lachnospiracea＿incertae＿sedis,Clostridium＿IV,Prevotella,Methanobrevibacter,Turicibacter and others detected in the cecum.We also found that supplementary feeding starter groups significantly increased the abundance of bacteria genus that were mainly involved in the utilization of starch and the production of propionate or butyrate in rumen,jejunum,ileum,and cecum of the yak calves.This response was included Prevotella,Oscillibacter,Anaerovibrio,Synergistes,Dialister,Clostridium Xl V and others in the rumen.Their such as Propionibacterium,Synergistes,Clostridium IV,Pseudobutyrivibrio,Prevotella,Succinivibrio and Bifidobacterium be found in the jejunum.We also detected Brachybacterium,Propionibacterium,Clostridium Xl Vb,Eubacterium,Faecalibacterium,Clostridium Xl Va,Synergistes,Anaerovibrio and Prevotella,which were excited in the ileum.And we found such as Synergistes,Eubacterium,Pseudobutyrivibrio,Prevotella,Turicibacter,Methanobievibacter and Ruminococcus in the cecum.While,supplementary feeding alfalfa hay significantly increased the abundance of bacteria genus associated cellulose and hemicellulolytic in yak calves,including Eubacterium,Butyrivibrio and Lachnospira in the rumen and Pseudobutyrivibrio,Saccharibacteria＿genera＿incertae＿sedis in the jejunum.Not only these,in the ileum,there were Saccharibacteria＿genera＿incertae＿sedis,Arthrobacter and Anaerovibr and Methanobievibacter,Olsenella,Vulcanilbacterium,Aquabacterium,Limnobacter,Caulobaceterand Tepidimonas in the cecum.To sum up,compared with maternal+grazing,the change of gastrointestinal microbiota regulated by replacer+supplementary feeding stater and alfalfa hay promoted the development of digestive tract function of yak calves,the changed microbiota improved the nutrient utilization and immune homeostasis level,and then improved the growth and development quality of yak calves.In conclusion,yak calves weaned at the age of 30 days,the early supplementary feeding based on feeding milk replacer significantly improved the dry matter intake of yak calves,supplemented the nutrients needed for growth and development,and improved the growth performance of suckling yak calves.The patterns of replacer+supplementary feeding increased the species and abundance of starch and fibrinolytic bacteria in the digestive tract of yak calves,the change of microbial community and fermentation products promoted the early development of digestive tract morphology and function,and improved the level of mucosal immune homeostasis.Which provided an important basis for the study of quality improvement and breeding technology of yak calves in plateau area.