Developing beef replacement heifers into productive mature animals requires nutritional strategies that support adequate growth, timely puberty, and optimal pregnancy outcomes. Direct-fed microbials (DFM), particularly spore-forming Bacillus species, can improve forage digestibility and host performance by modulating the gut microbial community. This 2-yr study evaluated whether daily supplementation with a Bacillus-based DFM mixture improved growth performance, fecal and vaginal microbial communities, and reproductive outcomes of Bos indicus-influenced beef heifers grazing warm-season grasses. Despite similar growth performance, heifers supplemented with the DFM showed earlier attainment of puberty, a tendency for greater pregnancy per artificial insemination (AI), and an earlier calving distribution compared with non-supplemented counterparts. Bacillus-based DFM supplementation also shifted fecal microbial communities toward greater abundance of fiber-fermenting and butyrate-producing bacteria, reduced fecal microbial diversity at timed-AI, and reduced vaginal abundance of methanogenic archaea throughout the study period. These findings suggest that Bacillus-based DFM supplementation may improve reproductive efficiency in developing beef heifers by modulating microbial communities in both the gastrointestinal and reproductive tracts.

Read the full article in the Journal of Animal Science.