Evaluation of Urea-Phosphate as a Source of Nitrogen and Phosphorus for Ruminants5

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Abstract
Three experiments designed to evaluate urea-phosphate as a source of nitrogen and phosphorus in ruminant rations were conducted. In an 8-week growth and slaughter trial with 24 twelve-week old Holstein calves, the phosphorous in urea-phosphate was found to be as well utilized as that from dicalcium phosphate. The basal diet contained 0.08% phosphorus, and the supplemented diets, 0.19%, on a dry basis. Two digestion and metabolism trials with wether lambs were conducted using semi-purified diets containing 20 to 25% crude fiber and either urea, urea-phosphate or soybean meal. The nitrogen from urea and urea-phosphate at a level of 40 to 45 percent of the total dietary nitrogen was as well utilized as the nitrogen from soybean meal at adequate levels of energy intake. At this level of feeding, urea-phosphate tended to depress intake and produced looser feces. Phosphoric acid, either as a component of urea-phosphate or when added with urea, suppressed the elevation of rumen pH and blood ammonia following the drenching of lambs with urea. Twenty-five units (gm. urea/45.4 kg. live weight) of urea as a drench resulted in death of lambs, while 40 units of urea-phosphate were required to produce toxicity. Blood ammonia was elevated with urea but not with urea-phosphate, suggesting a different mode or rate of action by toxic levels of urea-phosphate. Lesions of animals succumbing to urea-phosphate included severe degeneration of the liver and kidneys, a finding similar for animals dying of urea poisoning.