Effects Of Dietary Concentrate To Roughage Ratio On Digestive Tract Morphology And Microbial Diversity Of Fattening Tibetan Sheep

The purpose of this experiment was to study the effects of different concentrate to roughage ration on the production performance,digestive tract morphology,rumen fermentation parameters,rumen and intestinal microbial diversity of 3-month-old Tibetan lambs,so as to provide theoretical basis for reasonable concentrate to roughage ration in fattening period.210 healthy and similar 3-month-old Tibetan sheep were selected and randomly divided into 7 groups（30 sheep in each group）.They were fed diets with concentrate to forage ratio of 80∶20（group A）,70∶30（group B）,60∶40（Group C）,50∶50（Group D）,40∶60（Group E）,30∶70（Group F）and 20∶80（group G）respectively.The experimental period was 90 days and the pre feeding period was 10 days.The daily feed intake was recorded.Fasting weight was weighed and recorded at 8:00 in the morning of 0 d,30 d,60 d and 90 d,respectively.The average daily feed intake,average daily gain,feed to weight ratio and economic benefit were calculated.After the experiment,3 experimental sheep were randomly selected from each group for slaughter,rumen tissue samples and intestinal tissue samples were collected from the same site to make frozen sections,which were observed and measured under light microscope,rumen contents and intestinal food samples were stored in liquid nitrogen in the same site for microbial diversity determination.The results show that:1)During the experimental period,the body weight gain of group A was the highest（P<0.05）,and the total feed intake of group C was the highest;with the decrease of concentrate feed ratio,the feed weight ratio had a decreasing trend;by comparing the weight gain and feed intake of lambs,it was found that the economic benefit of group B was the best,and too low concentrate feed ratio would significantly reduce the production performance and economic benefit of lambs.2)Rumen keratinization layer thickness,rumen nipple density and height of Tibetan sheep in group D were significantly higher than those in the other groups（P<0.05）.The thickness of rumen muscularis in group F was significantly higher than that in other groups（P<0.05）.Too high concentrate roughage proportion（Group A）inhibited the development of intestinal villi,muscle layer and mucous membrane;the intestinal crypt depth of Tibetan lambs was positively correlated with the proportion of roughage in the diet（P<0.05）.Rumen NH₃-N,Propionate,Butyrate and Total volatile acid concentrations were positively correlated with the proportion of concentrate in the diet（P<0.05）,while the change trend of Acetate was opposite（P<0.05）.The development of rumen papilla and keratinized layer was better in group D during fattening.In group B,intestinal morphology developed to the best state and rumen fermentation was promoted.3)In the microbial diversity of rumen bacteria,Shannon index,ACE index and Chao1 index were significantly higher in group F,while Simpson index was significantly lower（P<0.05）.At phylum level,the relative abundance of Firmicutes decreased with the increase of sperm to crude ratio,and group A was significantly higher than the other groups（P<0.05）;at family level,the relative abundance of Lachnospiraceae was negatively correlated with ratio of concentrate to roughage（P<0.05）.Among the microbial diversity of rumen fungi,Ascomycota was the dominant phylum.The Basidiomycota of group B was significantly higher than that of the other groups（P<0.05）;there was little distribution of Neocallimastigomycota in high concentrate group（group A,group B,group C）（P<0.05）.At the family level:the change trend of Nectriaceae,Peniophoraceae and Lasiosphaeriaceae tended to be similar,which were significantly lower in low concentrate group（Group E,group F and group G）than in group B（P<0.05）;the Aspergillaceae and Myxotrichaceae in Group E were significantly higher than those in group B and group C（P<0.05）;the Sebacinaceae in group C was significantly higher than those in other treatment groups（P<0.05）.The increase of concentrate ratio（70∶30）could enrich the diversity and richness of bacteria and fungi in rumen.4)In intestinal bacterial diversity,ACE and Chao1 index showed similar trend,and the ratio of concentrate to roughage in Group E was significantly higher than that in other groups;at phylum level,the dominant phylum in all groups was Proteobacteria,and group C was much higher than that in other groups（P<0.05）;At the family level,Sphingomonadaceae was the dominant family,and the abundance of group C was higher than that of the other treatment groups（P<0.05）;The abundance of Xanthobacteraceae in group F was significantly higher than that in other treatment groups（P<0.05）;the abundance of Lachnospiraceae in Group E was higher than that in other treatment groups（P<0.05）.The functional genes of small intestinal bacteria are concentrated mainly in amino acid metabolism,carbohydrate metabolism,biofilm transport and so on.In the diversity of small intestinal fungi,Ascomycota was the dominant phylum in each treatment group,and group C,D and F were significantly higher than those in groups A and B（P<0.05）;Basidiomycota in group B was significantly higher than the other groups（P<0.05）.At the family level,Mortierellaceae was the dominant family of intestinal fungi in Tibetan sheep,and the proportion in group A and B was relatively high（P<0.05）;Aspergillaceae in groups C and D were significantly higher than those in other groups（P<0.05）;Nectriaceae in group B was significantly higher than that in other groups（P<0.05）.when the ratio of concentrate to roughage was 60∶40,small intestinal microorganisms were more suitable for colonization.In conclusion,in the short-term fattening process,when the ratio of concentrate to forage is 70:30,the experimental results in terms of economic benefits of production and colonization of digestive tract flora of Tibetan sheep are the best,while in the long-term fattening or the breeding of adult ewes,the appropriate reduction in the ratio of concentrate to forage is more conducive to the digestive tract health of Tibetan sheep.