Milk Urea as an Estimate of Urine Nitrogen of Dairy Cows and Goats

Abstract

In experiments with 14 dairy goats fed 8 different diets the urinary nitrogen excretion (g/day) was found to be related to milk urea nitrogen concentration (mg/100 ml) according to the equation y = 3.67 + 0.67 x; r ² = 0.64; CV = 15.6. In the case of 14 dairy cows yielding 3–37 kg of milk daily on various diets the corresponding equation based on afternoon milk was y = 24.5+10.9x; r ²=0.73; CV=13.8. The coefficient of determination (r ²) was found to be 0.94 when calculated from the mean values for each experimental period or diet (means from 3 or 4 cows). The urea/creatinine ratio of the urine gave a more accurate estimate of the total urinary nitrogen of an individual cow than blood or milk urea, (CV = 7.2 vs. 11.0 or 10.0). Plasma concentrations of urea and creatinine measured in 4 cows were not closely correlated. It is concluded that milk urea concentration in samples obtained from the regular milking may be used to estimate the urinary nitrogen excretion in groups of cows.