Effect of intravenous infusion of urea on nitrogen metabolism of steers

Abstract

Four 2-year-old steers with an initial weight of 599 kg (SD= 18.4) were used to study nitrogen recycling to the gastrointestinal tract. Urea was infused intravenously (0, .4,.8 and 1.2 g/kg MBW per day) in a 4 by 4 Latin square experimental design. Steers were fed a single diet containing 5.4 % crude protein. Plasma urea-N (PUN), rumen ammonia-N (RAN) and plasma ammonia-N (PAN) were increased linearly (P<.0001, P<.0002 and P<.0001, respectively) by increasing the amount of urea infused. Ammonia gradient across the rumen wall (the difference between unionized RAN and unionized PAN) tended to decrease linearly (P<.08) by increasing the infusion of urea, although it was negative for the 4 treatments. Dry matter intake (6.02 kg/day, P<.94) and dry matter digestibility (61.8%, P<.39) were not affected by treatment. Infusion of urea increased the ammonia concentration in duodenal contents (P<.03) and nitrogen excretion in feces (P<.058) and urine (P<.002). Nitrogen balance was increased by urea infusion (-9.4, 10.0, 14.1 and 20.6 g N/day, P<.008) and weight loss tended to decrease (- 10.9, -9.3, -6.4 and 2.7 kg/period, P<.10). Urea infusion successfully increased RAN and nitrogen supplied to the rumen microbes. Indirect evidence suggests that microbial protein supply to the host animal was increased by intravenous infusion of urea.