UREA UTILIZATION IN GROWING AWASI LAMBS FED HIGH OR LOW ROUGHAGE PELLETED DIETS

Abstract

Two experiments were conducted with 36 young Awasi wether lambs to study the effect of urea supplementation at 2.5%, as a complete soybean meal replacement in control pelleted rations containing 30 or 50% barley hay, on nitrogen utilization, blood and rumen metabolites and activity in the tissue of certain urea cycle enzymes; supplementary data on feed intake, growth rate, feed efficiency and activity of some urea cycle enzymes were also collected only for lambs on 30% roughage pellets with or without urea. Experiment 1 involved 20 lambs and consisted of a growth trial and two sets of digestion and metabolism trials during a period of 120 days, while experiment 2 included the enzyme assay along with a 60-day growth trial and one set of three metabolism trials with 16 lambs, half of which belonged to the urea group and were treated with a drench of ammonium bicarbonate during a 45-day preweaning period before the experiment. All growth trials were with the low roughage ration only. Lambs fed urea-supplemented ration in experiment 1 showed improved growth rate (P < 0.05) and feed efficiency without any change in ad libitum feed intake as compared to the soybean control, and the improvement was mostly during the last 60 days. Urea supplementation increased crude protein and ether extract digestibility in both high and low roughage rations while it increased crude fiber digestibility in the high, but decreased it in the low, roughage ration. Daily nitrogen retention increased significantly (P < 0.05) in the urea group fed low roughage diet without changing the efficiency of utilization of absorbed nitrogen, while the retention by the high roughage urea group did not differ significantly from the control (P > 0.05). Ammonia and urea concentrations in the blood showed significant increases as a result of urea feeding. In experiment 2, daily gain, feed intake, feed efficiency, nutrient digestibility and nitrogen balance did not show any statistically (P > 0.05) significant difference between treatments, but trends in the values were similar to those observed in experiment 1. No difference in the activities of urea cycle enzymes could be detected in the liver, rumen and intestinal tissues between treatments.