Is it necessary to supplement dairy cows at grazing ?

Grazed grass is a high nutritive value forage, inexpensive to produce and harvest and can be the only feed for a lactating dairy cow. Without supplementation, milk production and composition at grazing vary between animals and are dependant on cow genetic merit. But grazing conditions (stocking rate, pre- and post-grazing height) imposed by the farmer to improve grass utilisation does not allow the dairy cow to satisfy the total energy demand. Consequently, concentrate is now more efficient than in the past and often responses of one kg of milk to one kg of concentrate with declining milk fat content and increasing milk protein content are reported. Recent work at INRA has highlighted small variations in efficiency with different imposed grazing managements. At the same time, in the case of constant concentrate allocation, the efficiency is quite stable between cows producing 25 to 45 kg at turnout. With these results, it is possible to simplify the concentrate allocation method at grazing. As in winter feeding, the energy source of the concentrate has an influence on milk fat content but only at a high level of supplementation. Including protein rich ingredients, even protected, is only justified in the case of low crude protein content grass. Forage feeding at pasture is not necessary and can contribute to poor grass utilisation. Grazed grass and forage supplementation are well complemented only in periods of grass shortage or with very high stocking rates.