Effect of rumen degradable energy supplementation on forage utilization and performance of steers grazing stockpiled cool season perennial grass pastures

Abstract

Añez-Osuna, F., Penner, G. B., Larson, K., Jefferson, P. G., Lardner, H. A. and McKinnon, J. J. 2015. Effect of rumen degradable energy supplementation on forage utilization and performance of steers grazing stockpiled cool season perennial grass pastures. Can. J. Anim. Sci. 95: 255–265. The objective of this study was to evaluate the effects of supplementing rumen degradable energy using blended by-product pellets that differed in starch and degradable fiber content on forage utilization and performance of steers grazing stockpiled cool-season perennial grass (CSPG) pastures. Forty-five yearling crossbred steers (334±23.5 kg) stratified by body weight (BW) were randomly assigned to one of nine pastures (five steers/pasture) of mature cool-season perennial grasses. Each pasture was randomly assigned (n=3) to one of three treatments: no supplement (CON); low-starch/high degradable-fibre (LSHF; 40.3% starch; 29.5% NDF) pellet and high-starch/low-degradable fibre (HSLF; 48.6% starch; 22.8% NDF) pellet, both fed daily at 0.6% of BW (DM basis). The grazing period lasted 70 d (from early-August to mid-October). Over the 70-d study, forage CP decreased from 9.9±0.82 to 6.9±0.59% of DM and digestible energy content decreased from 2.6±0.04 to 2.2±0.04 Mcal kg−1of DM. Treatment did not affect forage utilization (P=0.50; 73.4±3.15%) or forage DM intake (P=0.90; 9.0±1.54 kg d−1). Final BW and average daily gain (ADG) were not different (P>0.05) between LSHF (435±6.4 kg and 1.4±0.10 kg d−1) and HSLF (439±10.4 kg and 1.5±0.14 kg d−1) treatments. However, supplemented steers had higher (P<0.05) final BW and ADG than the control steers (402±5.6 kg and 1.0±0.09 kg d−1). These results show that unsupplemented beef steers grazing stockpiled CSPG pastures were limited in both energy and protein intake and that supplementation with by-product feed pellets formulated to supply protein and energy either as starch or degradable fibre equally improved animal performance.