Characteristics of ruminal microbiota and metabolome in Holstein cows differing in milk protein concentrations.

This study aimed to assess the ruminal microbiome, metabolome, volatile fatty acid concentrations, and amino acid profiles of Holstein cows with different milk protein concentrations. Previous studies have reported that ruminal microbiota can affect the lactation performance of dairy cows. However, little is known about the composition and function of ruminal microbiota in dairy cows differing in milk protein concentrations. In this study, we collected the milk protein concentrations data of 1,025 Holstein cows for 10 mo on a commercial farm. Three groups of cows (n = 10 per group) with low, medium, and high milk protein concentrations were selected. We found that cows with long-term high milk protein concentrations had lower microbial diversity, relative abundances of specific ruminal microbiota, protease activity, and amino acid concentration in the rumen compared to the cows with long-term low milk protein concentration. Meanwhile, cows with long-term high milk protein concentration showed higher amino acid concentrations in the plasma and lower ammonia levels in rumen, plasma and milk than cows with low milk protein concentration. Our findings revealed the correlation between milk protein concentration and specific ruminal microbiota, and proposed a possibility that ruminal microbiota affected milk protein concentration by altering host amino acid profile.