Increased Yearling Weight Gain Is Associated with a Distinct Faecal Microbial Profile

SIMPLE SUMMARY: Gut microbial profiles have been shown to influence a range of physiological processes contributing to animal performance. In particular, gut microbiota have a close relationship with digestion and metabolism, indicating they may be correlated to weight gain. As previous studies have discussed, gut microbiota ranging from the rumen to the hindgut can influence and potentially indicate differences in important production traits such as milk composition in dairy cattle and feed efficiency in beef cattle. Therefore, the objective of this study was to characterise the faecal microbial profiles of Angus steers with high and low average daily gain (ADG) at both weaning and yearling stages. The results indicate that at yearling stage, there was a distinct difference in the faecal microbial profiles of steers with high or low ADG. Primarily, we observed a reduction in species richness and decrease in between-sample phylogenetic similarity in the high ADG group. ABSTRACT: Microbial communities inhabiting the gut have the ability to influence physiological processes contributing to livestock production and performance. Livestock enterprises rely on animal production traits such as growth performance for profit. Previous studies have shown that gut microbiota are correlated to growth performance and could even influence it. The aim of this study was to characterise the faecal microbial profiles of Angus steers with high and low ADG at both weaning and yearling stages by profiling 16S rRNA gene sequences from rectal faecal samples. When microbial profiles were compared in terms of relative abundances, LEfSe analysis, alpha diversity metrics, and beta diversity, at the weaning stage, few significant differences were found between the high and low ADG groups. However, at yearling stage, microbial profiles significantly differed between the high and low ADG groups. The relative abundances of eight phyla and six genera significantly differed between the two groups. Alpha diversity metrics showed a significant decrease (p = 0.001) in species richness in the high ADG group. Similarly, beta diversity analysis showed that samples clustered clearly according to high and low ADG groups at yearling stage, indicating that phylogenetic similarity between the two ADG groups was significantly reduced (p = 0.005).