Abstract:

This experiment was conducted to study the effects of dietary concentrate∶roughage ratio on rumen tissue morphology and microbial flora in fattening Tibetan sheep. Early weaned Tibetan lambs （n=210） were randomly divided into seven groups with 30 lambs in each group. The seven groups were fed diets with concentrate∶forage ratios of 20∶80 （A）， 30∶70 （B）， 40∶60 （C）， 50∶50 （D）， 60∶40 （E）， 70∶30 （F） and 80∶20 （G）. The experiment comprised a feed adaptation period of 10 days and a measurement period of 90 days. After the experiment， 3 sheep in each group were slaughtered and rumen tissue and rumen fluid samples were collected. Frozen sections were used to observe the development of rumen tissues， the thickness of the rumen muscle layer and keratinized layer， and the length， width and density of ruminal papillae. 16S rDNA gene sequencing was used to determine the identity of rumen microorganisms present， and the abundance and diversity index of rumen bacteria were analyzed. The results showed that： 1） The morphology of rumen tissue was significantly affected （P<0.05） by the dietary concentrate∶forage ratio. When the concentrate∶forage ratio was 50∶50， the thickness of the rumen keratinization layer， the density and height of the ruminal papillae were significantly higher than that of the other groups （P<0.05）. When the dietary concentrate∶forage ratio 30∶70， the thickness of the rumen muscle layer was significantly higher than that of the other groups （P<0.05）. 2） In this study， 299 OTUs were detected across the seven treatment groups， including 259 OTUs （86.7%） and 40 unique OTUs， including 14 unique OTUs in group F and 8 unique OTUs in group G. The Shannon index， Ace index and Chao1 index of group F were significantly higher than those of other groups， while Simpson index of Group F was significantly lower than that of other groups （P<0.05）. There was a significant difference in bacterial diversity among groups. 3） At the phylum level， the relative abundance of Firmicutes decreased with increase in the concentrate∶forage ratio， and the relative abundance of group A was significantly higher than that of other groups （P<0.05）. At the family level， the relative abundance of Lachnospiraceae was negatively correlated with the concentrate∶forage ratio， and the relative abundance of Prevotellaceae in group E was higher （P<0.05）. According to the rumen tissue phenotype and bacterial flora diversity， the rumen tissue morphology changed with the increase of concentrate level in the diet， and the development of the ruminal papillae and keratinized layers was inhibited to a certain extent. However， increased concentrate∶forage ratio （70∶30） enriched the bacterial diversity of the rumen.

Key words: ratio of concentrate to roughage, Tibetan sheep, rumen histology, 16S rDNA, rumen microbiota