In Vitro and In Vivo Comparisons on the Utilization of Urea, Biuret and Diammonium Phosphate by Sheep

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Abstract
In digestion trials with sheep fed rations consisting of 50:50 ratios of roughage to concentrates (primarily corn cobs, soybran flakes, starch and shelled corn), biuret and diammonium phosphate did not appear to be utilized as efficiently as urea in changeover type trials but the differences were not significant. Blood urea-N was higher when the animals were fed urea than when fed biuret. In an “adaptation” trial, sheep were fed similar rations supplemented with two levels each of urea and biuret for 94 days. There appeared to be an adaptation to biuret when apparent digestibilities were considered but not when nitrogen retention or biological values were considered. No similar phenomenon with urea was observed. Biuret feeding had no appreciable effect on rumen ammonia or blood urea, whereas urea raised both considerably. Biuret was utilized very poorly by starch digesting rumen bacteria taken from sheep “adapted” to biuret. Furthermore, microorganisms taken from urea or biuret “adapted” animals failed to release ammonia from biuret when incubated in vitro.