Excretion of Specific Urinary Nitrogen Metabolites for Evaluation of Nutritional Treatments

Abstract

Sixteen male Holstein calves were assigned to four treatments at 3 days of age. Treatments were whole milk, an all milk protein commercial replacer, a whey protein milk replacer, and a high fat whey protein milk replacer all fed at 10% of body weight. All treatments were isonitrogenous. Chopped wheat straw was fed ad libitum. Calves underwent preputial re-section for collection of urine. Five-day nitrogen balance trials were at 1, 5, 9, and 13 wk. Basic nitrogenous components of urine were separated with an amino acid analyzer. Analysis of body weights and straw intakes by balance period showed no differences. Nitrogen balance was lower for the whey protein and high fat milk replacers than for milk. Nitrogen digested was lower for commercial and whey protein milk replacers than for milk. Nitrogen retained was lower for the commercial, whey protein, and high fat milk replacers than for milk. Nitrogen excretion in urine and feces was greater for the commercial milk replacer treatment. The excretion of ornithine, arginine, lysine, 1-methylhistidine, and 3-methylhistidine was greater in the urine of the commercial and high fat milk replacer groups than in the urine of the milk group. Several ninhydrin positive compounds also were increased. Quantitative measurement of excreted basic nitrogenous compounds in urine may improve the evaluation of nitrogen metabolism in balance experiments.