Influences of urea fermentation potential on growth performance, dietary energetics, digestive function, and blood urea N in Holstein steers fed a finishing diet based on steam-flaked corn where metabolizable protein supply was otherwise in excess of theoretical requirement

Abstract

Objectives: This study was conducted to examine the effect of urea fermentation potential (UFP) on digestive function, BUN, growth performance, and dietary energetics, in steers fed a finishing diet based on steam-flaked corn containing 15% dried distillers grains with solubles. Materials and Methods: Four UFP levels were evaluated (−0.30, 0.10, 0.50, 0.90). The UFP levels were manipulated by dietary urea inclusion level of 1.20, 0.80, 0.40 and 0%, respectively (DM basis). Results and Discussion: Dietary UFP did not affect (P > 0.10) ruminal digestion of feed N. Ruminal starch digestion decreased with increasing UFP (linear effect, P = 0.02). Ruminal digestion of starch and OM tended to be maximal (quadratic effect, P ≤ 0.07) at dietary UFP of 0.1%. Increasing UFP decreased flow to duodenum of nonammonia-N (linear effect, P = 0.04), and microbial N (linear effect, P = 0.05). Duodenal flow of feed N was not affected (P = 0.18) by dietary UFP. Increasing dietary UFP decreased total-tract digestion of OM (linear effect, P = 0.02), starch (linear effect, P = 0.03), and digestible energy (linear effect, P = 0.03). Increasing dietary UFP decreased ruminal pH (linear effect, P = 0.01) 1 h after feeding. Thereafter, the influence of dietary UFP on ruminal pH was not appreciable. Increasing dietary UFP decreased ruminal ammonia-N 1 h after feeding (linear effect, P < 0.01) and tended (linear effect, P = 0.10) to decrease ruminal ammonia-N at 2.5 h after feeding. Thereafter, ruminal ammonia concentrations across treatments remained low, averaging 1.9 ± 0.2 mg/dL. The Effects of increasing dietary UFP on increases in plasma urea-N (linear effect P < 0.05) was appreciable throughout the 10-h feeding interval; this effect was more pronounced during the first 3 h after feeding. Dietary UFP did not affect (P = 0.78) DMI. However, decreasing dietary UFP from 0.90 to 0.50% enhanced (quadratic effect, P ≤ 0.04) ADG, gain efficiency, and dietary NE. At dietary UFP of ≤0.5, observed dietary NE was consistent (99%) with that expected based on diet formulation. Implications and Applications: Even when finishing diet formulations otherwise exceed MP requirements, dietary UFP level remains a relevant factor to optimize dietary energy use. Dietary UFP levels greater than 0.50% could negatively affect digestion, gain efficiency, and dietary NE use.