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 intake and animal performance, four zero-grazing experiments were carried out, two in spring/early summer and two in late summer. Grass was fertilized at three 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 libitum to three groups of 12 dairy cows in mid lactation. Reducing fertilizer N decreased crude protein content and in-vitro digestibility, but increased 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 intake. In one of the experiments carried out in spring, net energy intake of cows offered 150N grass was lower, resulting in lower milk yields. In late summer, cows consumed less 150N grass and produced less yields of milk, fat and protein compared to the other treatments. Except for milk production differences in S92, a reduction of N fertilizer from 450 to 300 kg/ha per year did not affect intake or milk production.