Urea, meat meal or lupins as nitrogen supplements to barley and hay diets for yearling cattle at two levels of body condition

Abstract

Weaner steers were fed to attain either fat score 1 or 2 by the time that they were 1 year of age. Animals at each fat score were then either slaughtered or fed ad libitum on a basal barley and hay diet containing 11% crude protein or similar diets supplemented by either urea, meat meal or sweet lupins to contain 13% crude protein in the dry matter. Those fed were slaughtered as they attained fat score 3. Compared with those starting at fat score 2, the yearlings at fat score 1 had the same daily feed intake and thus a 10% higher relative intake, grew 15% faster and required 11% less feed per kg liveweight gain. However, they required only 6% less feed per kg carcass weight gain, owing to their 1% lower dressing percentage. The diets supplemented with the three different sources of supplementary nitrogen gave similar improvements over the basal diet in intake, growth rate and efficiency, and there were no interactions between diet and fat score. It was concluded that both the National Research Council and Agricultural Research Council feeding standards underestimate the nitrogen concentration required in grain and hay diets to ensure maximum performance and efficiency by yearling cattle growing from 220 to 370 kg liveweight, and that supplements of either urea, meat meal or lupins providing an extra 2 percentage units of crude protein improve performance to a similar extent.