SOME EFFECTS OF RUMINAL INFUSIONS OF UREA AND UREA-SUCROSE ON UTILIZATION OF OAT STRAW BY COWS

Abstract

Four diets, straw, straw plus urea, straw plus urea and sucrose, and straw plus urea but with a different mineral supplement than fed with diets 1 to 3, were compared using rumen-fistulated cows. Urea or urea and sucrose were dissolved in water and administered as continuous ruminal infusions. Increases of about 29% in dry matter digestibility and 17% cellulose digestibility were obtained with urea but not with urea-sucrose. Bacterial protein in rumen fluid was increased by an average of 63% by both urea and urea-sucrose treatments. Rumen ammonia and blood urea levels were increased tenfold and threefold, respectively, by the urea infusion, but the response to urea-sucrose was only one-half as great. Sucrose appeared to be used as an energy source in preference to the straw, as indicated by the increased rate of urea utilization, but tended to depress intake and digestibility of straw as compared with urea only. Dry matter intake, nitrogen balance and total short-chain fatty acids were not significantly altered by the treatments, but all snowed response trends. Effects of dietary treatments on proportions of short-chain fatty acids in the rumen were not consistent.