Influence of Urea, Biuret and Starch on Amino Acid Patterns in Ruminal Bacteria and Blood Plasma and on Nitrogen Balance of Steers Fed High Fiber Purified Diets

Growing steers were fed purified diets in which nitrogen was supplied by either 4.7% urea or 4.9% biuret, and carbohydrate by either 87% wood pulp or 74% wood pulp plus 13% starch in a 4 × 4 Latin square designed experiment. Prefeeding blood and postfeeding (4 hours) ruminal samples were obtained following 30-day adaptation and 7-day excreta collection periods. Diets which contained urea were consumed more slowly. The amount of the urease activity in ruminal bacteria was reduced in steers fed urea. From steers fed biuret, rumen bacterial hydrolysates contained more alanine and blood plasma contained more glutamic acid. In vitro studies showed that ammonia concentrations of rumen culture contents collected throughout the day were on the average higher when urea was fed than when biuret was fed. In vivo, the concentrations of ammonia in ruminal contents were similar 4 hours after feeding in the steers fed the two nonprotein nitrogen sources. Starch added to the diet decreased fiber digestion and increased nitrogen retention. Starch increased blood plasma concentrations of valine, isoleucine and proline and decreased excretion of urinary nitrogen.