A new method to estimate microbial nitrogen escape from the rumen of the dairy cow

Rumen microbial N escape was estimated as the sum of the rumen fluxes of liquid and particulate associated microbial N. Rumen microbial N escape was calculated as the product of rumen pool size, rate of rumen passage and microbial concentration for both rumen liquid and particulate fractions. Dietary treatments that differed in rumen protein and carbohydrate availability were offered in three 2×2 Latin square design experiments with early lactation and late lactation cows. Differences in rumen microbial N escape (g/kg) DM intake were significant among treatments for early lactation cows. Measured daily rumen microbial N escape ranged from 153 to 438 g/day, varying with stage of lactation and rumen protein and carbohydrate availability, and were within the range of values reported using in vivo duodenal flow procedures. However, these measured values were not consistently predicted using any recent NRC equation.