Date of this Version
Two metabolism trials evaluated urinary allantoin excretion as a noninvasive marker of microbial crude protein flow from the rumen. In the first trial, both urinary allantoin excretion and duodenal purine flow increased as alfalfa intake increased. A positive linear relationship (r2 = .74) existed between the markers. In the second trial, an increase in the metabolizable energy supplied to the animal did not increase urinary allantoin excretion. We concluded that urinary allantoin excretion was an effective, noninvasive marker of microbial crude protein supply.