Comparison of the rumen bacterial community, rumen fermentation and growth performance of fattening lambs fed low-grain, pelleted or non-pelleted high grain total mixed ration

Abstract

This study aimed to compare the rumen bacterial community, rumen fermentation and growth performance of fattening lambs fed non-pelleted low grain, non-pelleted high grain or pelleted high-grain total mixed ration (TMR) in Hu sheep. Fifteen male lambs were allocated into 3 groups (n = 5 for each). One group (CON) received a low-grain non pelleted TMR (30% concentrate), the second group (HG) received a high-grain non-pelleted TMR (70% concentrate), while the third group (HP) received the same high-grain TMR in a pelleted form. The composition and CowPI predicted function of ruminal digesta-associated microbiome, rumen fermentation parameters and growth performance were examined. The animals of the HG group showed a significantly higher average daily gain (P = 0.032) and body weight gain compared to the CON group (P = 0.032). While there was no significant difference between HG and HP in any of the growth performance parameters. As compared with the HG group, rumen pH of the HP group was lower (P = 0.012), while lactate concentration was higher (P = 0.024). The unweighted unifractional principle coordinates analysis and the analysis of the molecular variance (AMOVA) revealed that all groups clustered separately from each other. All the alpha diversity estimators were decreased in HG compared to CON as well as in HP compared to HG. Bacteroidetes and Firmicutes were the predominant phyla in all groups and the abundance of Fibrobacteres was significantly decreased in the HP group compared to the HG group (P = 0.047). At the genus level, as compared with the HG group, pelleting resulted in a decrease in the percentage of unclassified BS11 gut group and Succiniclasticum, while it led to an increase in the abundance of some simple sugar fermenters like Megasphaera (P = 0.008), Olsenella (P = 0.007), Dialister (P = 0.009) and Sharpea (P = 0.019). Among the predominant OTUs, the proportion of some OTUs belonging to the Prevotella species increased in the HG group with a severe decrease in the HP group. The CowPI predicted functional profile of the rumen microbiome revealed the enrichment of the pentose phosphate pathway in the HP group only. In summary, this study showed that pelleting the high-grain TMR altered the rumen fermentation and amplified the ruminal microbiome simple sugar utilization.