Grazing system and botanical diversity effects on the quality of herbage consumend by dairy cows

Selection and foraging behaviour of 9 Holstein and 9 Monbéliarde dairy cows were compared between continuous (CG) or rotational (RG) grazing management on mountain pastures in the centre of France, over a two-week period. The CG plot was a species-rich heterogeneous pasture while the RG plot (divided in 2 paddocks) was a long-term grassland. Botanical composition, pasture structure, stem and leave proportion and nutritive value of grazed patches were measured. On the RG system an increase in grazing frequency of shorter patches to the detriment of higher ones was observed, along with a decrease in leave proportion and in forage quality. In spite of the great botanical diversity, on the CG system, the proportion of forbs and legumes in cow diet was very small. At the end of the exploitation of CG plot an increase in selection of short selected patches and in their leave proportion, and consequently in nutritive value, was shown, suggesting that cows select regrowth vegetative patches. The CG system allowed cows to graze herbage with a quite constant nutritive value during the short period, when compared to RG