Influence of milk transition on the early developing gut microbiome in pre-weaned calves

We investigated the drastic changes of intestinal microbiome composition from day 0 to day 56 after birth. In this study, calves were fed colostrum on day 0 after birth, whole milk from day 2 to day 5 days, and milk replacer from day 6. We found a temporary decrease in the Chao1 index of diversity from day 6 to day 8, followed by an increase in diversity. Interestingly, the number of calves with diarrhea increased in the second week (day 8 to day 14) after birth. Speculating an association between the transition of milk, we compared the milk composition between whole milk from day 4-5 and milk replacer by an untargeted metabolomic analysis and discovered the relative abundance of hypotaurine and D-xylose to be significantly higher in whole milk. We also found low levels of Collinsella in the intestinal microbiome and high levels of phenol and homocysteine in the plasma to be associated with diarrhea in early calves. Taken together, this study suggests links between the temporary instability of intestinal microbiome during the milk transition with diarrhea in pre-weaned calves.