The Value of Urea in Protein Supplements for Cattle and Sheep

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Abstract
Two protein supplements, originally prepared in pellet form for range feeding, were compared in maintenance, wintering and fattening rations fed to steers and lambs in nitrogen balance trials. Urea supplied 25 percent of the total nitrogen in one supplement and 50 percent in the other one. The value of the nitrogen contributed by urea in these supplements was determined by feeding the same supplements, without urea, in identical rations. Nitrogen retention by steers and lambs on each type of ration was increased by the additional nitrogen supplied by urea in the supplements. The 50 percent urea-nitrogen supplement was as efficient as the 25 percent supplement in promoting these retentions. There were feed refusals by steers, however, when the 50 percent supplement was fed in wintering rations. Lambs appeared to be more efficient than the steers in utilizing urea nitrogen. The apparent digestibility of ration nutrients other than protein (N×6.25) was unaffected by urea. Feeding the 25 percent urea-nitrogen supplement at less frequent intervals, on alternate days as compared to daily and twice daily, had no effect on urea utilization by steers. No ammonia could be detected in the expired air of steers following the feeding of urea.