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 p rotein 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 NE(m), referred to as high-energy and low-energy, res pectively) and protein source (ring-dried blood meal [BM] vs soybean m eal [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 digestib ility (CPD) were exceptionally high during wk 1, when DMI was approxim ately 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 per formance data indicate that, compared to SBM, feeding BM may improve A DG 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 n ot adversely affected. Therefore, it seems that the reduced feed intak e and growth rate normally seen during the first 2 wk in the feedlot i s not caused by a reduction in diet digestibility.