The aim of our study was to determine the effect of diets with different types of roughage on the ruminal microbial metabolite profile in dairy cows. Holstein dairy cows were fed a diet containing either corn stover (CS group) or a mixture of alfalfa hay, Leymus chinensis hay and corn silage (MF group) at 0700 and 1900 h daily. Rumen fluid was sampled from each cow through a ruminal cannula at 0630 and 1030 h, and the mixed ruminal fluid from 3 day in each cow was analysed using nuclear magnetic resonance (NMR) spectroscopy. A multivariate analysis revealed a significant difference between the ruminal metabolome of the CS and MF groups at both time points. The MF group had higher levels of acetate, valerate, hydrocinnamate and methylamine and lower levels of glucose, glycine, propionate and isovalerate than those in the CS group. Our results showed that different types of roughages can significantly influence the ruminal microbial metabolome, especially with regard to organic acids, amines and amino acids.Significance and Impact of the Study:
The microbial metabolites in the rumen provide nutritional precursors that are critical for general health and milk production in dairy cows. However, studies of the effect of diet on ruminal microbial metabolism are scant. In our current study, we analysed the ruminal microbial metabolite profile of cows fed different types of roughage. We found that the ruminal microbial metabolite profile of cows fed a mixed-roughage diet differed significantly from that of cows fed a single type of roughage. Certain metabolites, such as acetate, hydrocinnamate and methylamine, were closely correlated with specific types of roughage. Our findings provide insight into the effects of different roughages on ruminal microbial fermentation in dairy cows.