부산대학교 도서관

Two trials were conducted to evaluate the influence of supplemental urea withdrawal on characteristics of digestion(Trial 1) and growth performance (Trial 2) of feedlot cattle during the last 40 days on feed. Treatments consisted of asteam-flaked corn-based finishing diet supplemented with urea to provide urea fermentation potential (UFP) of 0, 0.6,and 1.2%. In Trial 1, six Holstein steers (160 ± 10 kg) with cannulas in the rumen and proximal duodenum were used ina replicated 3 × 3 Latin square experiment. Decreasing supplemental urea decreased (linear effect, P ≤ 0.05) ruminalOM digestion. This effect was mediated by decreases (linear effect, P ≤ 0.05) in ruminal digestibility of NDF andN. Passage of non-ammonia and microbial N (MN) to the small intestine decreased (linear effect, P = 0.04) withdecreasing dietary urea level. Total tract digestion of OM (linear effect, P = 0.06), NDF (linear effect, P = 0.07),N (linear effect, P = 0.04) and dietary DE (linear effect, P = 0.05) decreased with decreasing urea level. Treatmenteffects on total tract starch digestion, although numerically small, likewise tended (linear effect, P = 0.11) to decreasewith decreasing urea level. Decreased fiber digestion accounted for 51% of the variation in OM digestion. Ruminal pHwas not affected by treatments averaging 5.82. Decreasing urea level decreased (linear effect, P ≤ 0.05) ruminal N-NHand blood urea nitrogen. In Trial 2, 90 crossbred steers (468 kg ± 8), were used in a 40 d feeding trial (5 steers/pen, 6pens/ treatment) to evaluate treatment effects on final-phase growth performance. Decreasing urea level did not affectDMI, but decreased (linear effect, P ≤ 0.03) ADG, gain efficiency, and dietary NE. It is concluded that in addition toeffects on metabolizable amino acid flow to the small intestine, depriving cattle of otherwise ruminally degradableN (RDP) during the late finishing phase may negatively impact site and extent of digestion of OM, depressing ADG,gain efficiency, and dietary NE.