LAUSR

The nature of weaning is considered as the most stressful period experienced by dairy calves and has been known to negatively affect calf growth and intake. The objectives of this study were to investigate the shift of rumen and colon mucosa-associated microbiota in dairy calves fed with a high plane of milk pre- and post-weaning, and whether such shifts are associated with rumen fermentation and growth performance. Six Holstein dairy bull calves were ruminally cannulated at the second week of life followed by weaning at the end of week 6. Ruminal and colon tissue samples were biopsied at the end of week 5, 7 and 12 to determine the bacterial community changes, and rumen content was collected at the same time to measure rumen fermentation parameters. QIIME2 was used to analyze microbial profiles and R studio software was used to determine the microbial changes and its relationship with phenotypic measures. Age-dependent profiles were observed for the colon mucosa associated microbiota but not for rumen mucosa associated microbiota, indicating that varied responses to weaning transition exists between colon and rumen mucosa associated microbiota. As calves aged, higher abundance of taxa such as Delftia (associated with hexadecanoic acid production) and lower abundance of Veillonella (associated with short-chain organic acids utilization) were detected in the colon mucosa. The rumen also displayed taxonomic changes with decreases in Pseudobutyrivibrio in older calves. In addition, we identified significantly positive correlations between Prevotella associated with rumen mucosa and average daily gain, Isovalerate and Isobutyrate, suggesting that this genus may promote rumen fermentation during weaning transition. Our findings suggest that weaning transition affects rumen and colon mucosa-associated bacteria, and some of the rumen mucosa-associated microbiota promote rumen fermentation during this period, which may have long-term effects on animal health and productivity.