The level of plant biodiversity in pasture modifies dairy cow digestive processes, rumen and faeces microbiota and milk composition ; Le niveau de biodiversité végétale des prairies modifie les processus digestifs, le microbiote ruminal et des fèces des vaches laitières et la composition du lait

Séance : Alimentation ; International audience ; To study the interactions between the plant biodiversity of pastures, ruminants, their microbiota and their products, an in vivo and in vitro experiment was carried out in the spring 2018. After a 5-week adaptation period on a common plot, 2 groups of 7 dairy cows were led for 4 weeks on 2 plots with contrasting levels of plant biodiversity: LD (19 species, mainly grasses) and HD (56 species, mostly dicots). Samples of grass selected by the cows (simulated bites), rumen fluid, faeces, and milk were taken at the end of the experimental periods, respectively. Milk production and protein and fat concentration were similar between treatments. The grass from group HD was more fibrous and had a higher total tannin content. Grass total fatty acids (FA) and C18:3 n-3 contents were higher for LD. Total gas production during in vitro ruminal fermentation of HD grass was lower compared to LD, this being probably due to the inhibition of bacterial proliferation by tannins, which also protected the digestion of the dry matter of the HD group compared to LD. Ruminal fluid of HD cows differed from that of LD cows by a lower concentration of total FA but a higher proportion of polyunsaturated fatty acids (PUFA). This suggests a less complete biohydrogenation of dietary PUFA induced by tannins. The β-diversity, which considers the equipartition of species, showed differences between the bacterial and fungal communities of the ruminal liquid and the faeces of the cows between the 2 treatments. The FA profile of milk from LD cows is distinguished by a higher concentration of C18:2 c9t11. Moreover, the quantity of C18:3 n-3 is not significantly different between the treatments, despite the marked differences on grass. The lower total FA and n-3 content of the grass from the HD group could have been compensated by the protective role of tannins in the rumen. ; Pour étudier les interactions entre la biodiversité végétale des prairies, les ruminants, leur microbiote et leurs produits, ...