Urea Utilization by Young Dairy Calves as Affected by Chlortetracycline Supplementation

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Abstract
Forty-eight, 2-day-old male and female calves representing the Holstein and Jersey breeds were raised to 86 days of age on a limited milk-hay-starter system to study the effect of chlortetracycline on urea utilization at 3 levels of protein equivalent intake. Four experimental starters ranging from 6.5 to 15.3% protein equivalent were fed with and without chlortetracycline supplementation. Highest average daily gains were made by calves on the 12.1% protein equivalent starter with chlortetracycline. The growth of calves increased as the protein equivalent level of the starter increased up to the 12.1% protein equivalent starter. Chlortetracycline did not spare dietary N in this study, but did significantly increase average daily gains, skeletal growth, and feed efficiency. It had no significant effect on apparent digestibility of any ration nutrient, N retention, or blood levels of plasma protein and urea N. Coefficients of dry matter and crude protein digestibility, as well as N retention values, were significantly lower for calves on the 6.5% protein starter than for any of the other groups. The trend was for increased protein digestibility as the level of protein equivalent in the starter increased.