Effects of grassland biodiversity on digestive process, milk composition, and microbiota of dairy cows

The effects of pasture botanical biodiversity on rumen and faecal microbiota composition and milk fatty acids profile was studied in an in vivo and in vitro experiment carried out with 2 groups of 7 dairy cows. Cows were led for 4 weeks on 2 plots with high (HD) and low (LD) levels of plant biodiversity. The herbage from HD was more fibrous and had a higher total tannin content, but lower total fatty acids and C18:3 n-3 contents than LD. Samples of simulated bites, rumen fluid, faeces, and milk were collected at the end of week 4. Though species richness of bacterial and fungal communities were similar, their composition differed and discriminative species have been pointed out for each level of biodiversity. Total gas production and CH4 proportion during in vitro ruminal fermentation of HD herbage was lower than LD, probably because of the partial inhibition of bacterial activity by tannins. Remarkable was the comparable proportion of C18:3 n-3 in milk, despite the lower total fatty acids and C18:3 n-3 content of HD herbage. Plant metabolites could have partially inhibited the activity of ruminal bacteria responsible for lipid biohydrogenation.