Effects of supplemental urea sources and feeding frequency on ruminal fermentation, fiber digestion, and nitrogen balance in beef steers
2012
Alvarez Almora, E.G. | Huntington, G.B. | Burns, J.C.
The objective of two experiments was to evaluate non-protein N supplementation with protected urea sources in terms of rumen fermentation products, nutrient digestibility, and N balance in ruminally fistulated beef steers (initial bodyweight 239±18kg) fed switchgrass hay. Experiment 1 compared urea with Optigen II®, and Experiment 2 compared urea with RumaPro®. In both experiments, supplements (400g/kg of daily dietary dry matter) were fed once daily or every 2h in a balanced design. Supplements contained soybean hulls, corn grain, vitamins, and minerals as well as non-protein N sources. Non-protein N provided 0.18g/g of dietary N. Switchgrass hay was fed once daily, at the same time as the supplement in the once-daily treatments. Dry matter intake (4.1kg/d in Experiment 1, 4.5kg/d in Experiment 2), dry matter digestibility (P<0.25, 0.58±0.014g/g in Experiment 1, 0.58±0.010g/g in Experiment 2), N balance (P<0.83, 11.3±1.9g/d in Experiment 1, 11.8±3.6g/d in Experiment 2), ruminal ammonia concentrations (P<0.29, 15.2±1.4mM in Experiment 1, 11.8±0.6mM in Experiment 2), and ruminal short-chain fatty acid concentrations (P<0.13, 77.7±3.0mM in Experiment 1, 75.4±3.0mM in Experiment 2) were not affected by feeding protected urea sources. Providing a steady supply of ruminally degradable N by feeding supplement every 2h vs once daily decreased ruminal ammonia concentrations by approximately one-half by 4h after feeding hay (P<0.01 in both experiments) and increased (P<0.02 in Experiment 1, P<0.08) in Experiment 2) apparent digestibility of dry matter (0.58–0.62 in Experiment 1, 0.56–0.61 in Experiment 2) and dietary fiber components.
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