392 Gut bacterial communities and their association with production parameters in beef cattle

Within the past decade, the development and use of novel nutritional, genomic, and genetic improvement technologies has promoted and lead to great increases in the genetic propensity of beef cattle for a variety of traits including growth, carcass composition, and specifically feed efficiency. However, the optimization of feed efficiency has primarily focused on host genetics, management, and diet. The rumen and lower gastrointestinal tract (GIT) contain diverse microbial ecosystems that are essential for the host to digest plant material and regulate nutrient uptake and utilization, necessitating their examination to fully understand the microbial-associated interactions throughout the gut with production parameters. To assess the association of the microbial community with variation in feed efficiency, ADG, and average daily DMI (ADFI), we examined the microbial community of the GIT from steers differing in feed efficiency using deep 16S rRNA gene-based community profiling. Steers were selected from 2 contemporary groups and were ranked based on their standardized distance from the bivariate mean (ADG and ADFI), assuming a bivariate normal distribution with a calculated correlation between ADG and ADFI. Four steers with the greatest deviation within each Cartesian quadrant were sampled (n = 16/group; 2 groups). Bacterial 16S rRNA gene amplicons were sequenced from the GIT content using next-generation sequencing technology. Bacterial diversity and richness metrics revealed no differences among the quadrants. However, finer changes in the relative abundance of microbial populations and operational taxonomic units did reveal differences between feed efficiency groups (P < 0.05), including shifts in dominant phyla and functionally significant genera in several segments of the GIT such as Proteobacteria (P = 0.030) and Butyrivibrio (P = 0.019) in the jejunum. These studies suggest the GIT microbial community differs at the 16S level in cattle that vary in ADG, ADFI, and feed efficiency; however, it is not clear whether host factors are driving changes in the microbiome or changes in the microbiome are contributing to differences in feed efficiency.