Effects of energy density and protein source on diet digestibility and performance of calves after arrival at the feedlot.

Sixty Angus crossbred steers (initial BW, 237 kg) were used in a 2 x 2 factorial experiment to determine the effects of energy density and protein source in receiving diets on steers performance and total tract nutrient digestion. The factors compared were energy density (1.80 vs 1.48 Mcal/kg of NEm, referred to as high-energy and low-energy, respectively) and protein source (ring-dried blood meal [BM] vs soybean meal [SBM]). Diets containing BM resulted in a 10.6% greater (P < .09) ADG and a 7.6% improvement (P < .05) in efficiency of feed utilization compared with those containing SBM. High-energy diets resulted in an 8.7% improvement (P < .05) in feed efficiency vs low-energy diets. Dry matter digestibility (DMD), NDF digestibility (NDFD), and CP digestibility (CPD) were exceptionally high during wk 1, when DMI was approximately 1.5 kg/d. Nutrient digestibility declined during wk 2 and 3, as intake increased, before stabilizing between wk 4 and 6. Additionally, NDFD was not consistently lower (P > .10) during this study for high-energy diets than for low-energy diets. The results of the overall performance data indicate that, compared to SBM, feeding BM may improve ADG and feed efficiency during the receiving period when dietary CP is approximately 13%. Additionally, DMD, NDFD, and CPD were higher on d 7 than at any other time, indicating that by d 7 ruminal function was not adversely affected. Therefore, it seems that the reduced feed intake and growth rate normally seen during the first 2 wk in the feedlot is not caused by a reduction in diet digestibility.