Metabolic Fecal Nitrogen in Ruminants Estimated From Dry Matter Excretion

Relationships between dry matter (DM) and nitrogen (N) intakes and excretions were examined using digestibility data from 45 rations fed to sheep and cattle. The proportion of total variation due to regression was greater when N intake was expressed as a function of DM excretion than as a function of DM intake. Nitrogen excretion was expressed by the equation y = −0.021x 2 + 0.137x + 0.891, where y = g N excretion per 100 g of fecal DM and x = g N intake per 100 g fecal DM. Extrapolating N excretion to zero N intake, the point of intercept at y = 0.891 g N per 100 g of fecal DM excretion is suggested as a measure of metabolic fecal nitrogen independent of the hay to concentrate ratio of the ration.