Metabolism of Urea Nitrogen and Adaptation response Trends in the Growing Weather and Steer

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Evans J. L.
Karue C. N.
Welch J. G.
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Two trials were conducted to study the utilization of urea nitrogen (N) and the adaptation response to ration urea. In Trial 1, four yearling wethers were placed in a 4 x 4 Latin Square treatment arrangement with IS-day periods, and fed a basal ration (B); B plus urea mixed, (M); B plus urea sprayed, (S); and B plus urea orally drenched (D). In Trial 2, two groups of three steers each were used to compare the effect of mixing the urea into the ration to the spraying of a water solution of urea on the feed at feeding time. The design was a single reversal conducted during two 35-day periods. In Trial 1 after taking into consideration the contribution of the B to retained N, the percentage of ingested urea N retained from urea was 55, 64 and 60 in rations M, Sand D, respectively. Spraying of urea caused a 20 per cent increase (p<0.10) in retained N over the urea-mixed ration. Differences between M and S were attributed to urinary fraction excretions; spraying reduced urea N excretions. The increase in urea N excretion in sheep fed the urea-mixed versus the urea-sprayed indicated a possible increase in the rate of ruminal hydrolysis of urea. Urea N excretion was negatively correlated to ammonia N excretion, with r = - 0.80 and -0.72 for wethers and steers, respectively. By changing the ingested N to below maintenance,some wethers excreted urea N equal to or lower than ammonia N. Retained N appeared to be regulated by changes in the fractions of urinary N excreted. In both wethers and steers after a sudden change in ration or level of ration N, the change in urea N excreted accounted for 67 to 80 per cent of the total change in urinary N losses. Changes in urinary N fractions appeared to be more related to N metabolism responses. The change in urea N excretion was very rapid; this is regarded as a short-term adaptation response. Slow changes in non-urea N excreted were observed only in sheep, and were regarded as indicative of a long-term adaptation response, which resulted in a small increase in N retention as long as the decrease in ammonia N and undetermined N fractions was greater than the corresponding increase in urea N excretion.
East African Agricultural And Forestry Journal, XXXVI (NO1), p. 88-93