Effect of reducing nitrogen fertilizer on grassland on grass intake, digestibility and milk production of dairy cows

To quantify the effect of a reduction in nitrogen fertilizer on grass intak e and animal performance, four zero-grazing experiments were carried out, t wo in spring/early summer and two in late summer. Grass was fertilized at t hree levels of N fertilizer, 450, 300 and 150 kg/ha per year and harvested daily at dry matter yields between 1500 and 2000 kg/ha. Grass was fed ad Li bitum to three groups of 12 dairy cows in mid lactation. Reducing fertilize r N decreased crude protein content and in-vitro digestibility, but increas ed sugar content in grass. Overall, in the spring experiments, a reduction in N fertilization from 450 to 150 kg/ha per year did not affect grass inta ke. In one of the experiments carried out in spring, net energy intake of c ows offered 150N grass was lower, resulting in lower milk yields. In late s ummer, cows consumed less 150N grass and produced less yields of milk, fat and protein compared to the other treatments. Except for milk production di fferences in S-92, a reduction of N fertilizer from 450 to 300 kg/ha per ye ar did not affect intake or milk production. (C) 2000 Elsevier Science B.V. All rights reserved.