Effects of management practices prior to and during ensiling and concentrate type on nitrogen utilization in dairy cows

Three experiments with a total of 18 multiparous Holstein-Friesian dairy co ws in early to mid lactation were used in incomplete changeover designs wit h four periods consisting of 4 wk each. The objectives of the experiments w ere to investigate the effects of 1) grass management practices prior to en siling and 2) concentrate energy sources on animal performance and N utiliz ation and suggest ways in which the annual N excretion can be reduced. In t he first experiment, four silages were prepared as early-cut material from grass that was fertilized with either 75 or 150 kg of N/ha. Two other silag es mere prepared from the latter but harvested 2 mk later. Within each sila ge type, both direct cut and wilted silages were produced. In the second ex periment, starch-based and fiber-based concentrates were offered with the t hree wilted silages used in the previous experiment. In the third experimen t, barley-based and corn-based concentrates were offered with three silages that had been treated with different additives at the time of ensiling. Ne ither dry matter intake nor milk yield were significantly affected by eithe r silage or concentrate type. Milk protein content and yield, however, were higher in silages made from medium fertilized grass and also increased wit h increased starch content of the concentrate. Grass management and diet af fected the amount and form of N excreted. Use of nitrogen fertilizer at low er than 75 kg of N/ha and feeding less degradable starch concentrate is rec ommended for mitigation of N pollution, especially in the form of urine N b y dairy cows in intensive farming.