Nutritional Responses of Calves Fed Milk or a Milk Replacer

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Abstract
The nutritional responses of young male dairy calves fed whole milk or a commercial milk replacer were measured from 3 days postnatal to 14 wk age of weaning. Treatments were whole milk or milk replacer at 12 or 8% of body weight or at a constant intake of 8 l daily. Chopped wheat straw was fed ad lib. Preputial resection was performed in the calves during the 1st wk of life to allow for clear separation of urine and feces during the experiment. The relationships between the excretion of several nitrogenous compounds and N balance were studied. Calves went through 4 N balance trials during the 13 wk experimental period. Most of the differences in changes of body weight and daily gain were related to amounts of whole milk or milk replacer fed. With 8% milk replacer less straw was consumed than with the 8% whole milk. Less N was digested and retained on milk replacer. Fecal N excretion was increased by the high intake of milk replacer. Milk replacer promoted growth comparable to whole milk, but its protein was not of equal nutritional value. Consistent changes across all balance periods were the effects on the excretion of total urinary N. A more critical evaluation of the nitrogenous components of urine may be useful in evaluating N metabolism in the young ruminant.