Effect of Nitrogen Solubility on Nitrogen Lactating Dairy Cattle

Abstract

N-balance trials (3) were used to measure N utilization in lactating dairy cows. In each trial, the basic diet was a complete feed containing 55% corn silage and 45% grain mixture (dry-matter basis). The crude protein contents of the complete diets in trials 1, 2, and 3 were 12, 13, and 15%, respectively. Four high-producing Holstein cows similar in age and producing ability and within 30-45 days postpartum were used in each 12 wk trial in a Latin-square experimental design. Urea was the treatment variable supplying approximately 0, 8, 16, or 24% of the total dietary N. The measured solubility of the N in the diets ranged from 31.5-48.7%. The data were fitted to a multiple linear-regression model to determine coefficients of N utilization. The utilization coefficients for soluble N and insoluble N were relatively constant across the 3 trials, but in each trial utilization coefficient for insoluble N was greater than for soluble N.