Nitrogen-containing fertilisers restrict grain intake by cattle

Abstract

Supplements of barley, a barley-lupin mix (BL), or lupin grain containing urea plus ammonium sulfate (4% + 0.5%, low N; 6% + 1.0%, high N) were offered ad libitum to Holstein-Friesian steers. Supplement intake was restricted by increasing the amount of urea and ammonium sulfate (average intake of 1.7 and 1.4 kg DM/day.100 kg LW for cattle offered low and high N supplements). Supplement intakes were 14-56% greater than predicted from previous studies. Despite the high N content of the diet consumed by steers offered supplements containing lupin (up to 4.8% N with the high N supplement), feed conversion efficiency (FCE) of these cattle was better (P<0.01) than for cattle offered barley supplements (5.3, 5.8, 6.1 kg DM/kg LW gain for lupin, BL, barley). In another experiment, Holstein-Friesian steers offered grain immediately before an ad libitum supplement of barley containing 8% urea consumed 30-50% more grain than those without immediate prior exposure to grain. When the intakes of Holstein-Friesian steers offered ad libitum supplements of either barley or lupin containing either 8% urea or 5.7% diammonium phosphate (DAP) were compared, supplement intakes across grains averaged 1.3 and 0.6 kg DM/day. 100 kg LW. These levels of urea and DAP were predicted to result in similar intakes. However, to achieve a desired level of supplement intake, less DAP was required than urea. Both liveweight gain and FCE were 22-24% greater for cattle offered lupin than those offered barley supplements. Adding urea at 0, 0.5, or 1.0% to a barley supplement containing 4% DAP did not affect supplement or hay intakes by Holstein-Friesian steers, which averaged 0.8 and 1.7 kg DM/day.100 kg LW, respectively. Liveweight gain and FCE were increased by 25% by adding urea to a barley supplement containing DAP. Finally, 3 different methods of introducing a grain supplement containing DAP to Holstein-Friesian steers were compared: a 4-phase, 16-day introductory period; a 2-phase, 7-day introductory period; no introductory period. In steers with and without immediate prior exposure to grain, neither method of introduction nor previous exposure to grain affected supplement intake, liveweight gain, or FCE.