The effect of two contrasting grazing managements and level of concentrate supplementation on the performance of grazing dairy cows

The grazing management of dairy cows is characterised by practices that vary greatly in terms of stocking rate, nitrogen fertilisation and supplementation. The objective of this 6-year experiment was to establish the response by dairy cows to increasing amounts of concentrate supplement under two contrasted rotational grazing systems. Each year, 30 cows were assigned to a Severe grazing system aimed at maximising milk production per hectare with high annual nitrogen input (280 kg N.ha(-1)) and a high stocking rate. Another 30 cows were assigned to a Lax grazing system characterised by a lower input (120 kg N.ha(-1)) and stocking rate aimed at offering a greater quantity of grass per animal per day. From 1995 to 1997, four moderate levels of concentrate supplementation (0, 1.4, 2.8 and 4.0 kg) adjusted according to the milk yield of the cows at turnout were compared. From 1998 to 2000, higher quantities of concentrate (0, 2, 4 and 6 kg) maintained at a flat rate between cows were compared. The Lax grazing system led to a 0.8 to 1.0 kg increase in milk yield (P < 0.0001) per cow per day without any significant modification of milk fat and milk protein content, compared to the Severe grazing system. Compared with the Severe treatment, the Lax treatment reduced cow grazing days by 160 days per ha and milk production by 3225 kg per ha. In both systems, concentrate supplementation made it possible to increase milk yield, with an efficiency of close to 1 kg of milk per kg of concentrate, as well as increasing milk protein content and live weight gain. The milk fat content decreased only in the last three years of the experiment, following an increased concentrate supplementation. All these animal responses remained linear up to the maximum amount of concentrate offered; there was no variation between cows supplemented with the same concentrate level. This multi-annual experiment confirms the importance of making the best possible use of herbage produced by adapting the stocking rate to achieve a post grazing sward height of 5 to 6 cm during the grazing season. With an increased genetic potential of the dairy herd, high individual cow performance at grazing can be attained by the use of concentrate supplementation.