Rumen Undegradable Protein Supplementation Effects on Forage Characteristics and Performance of Early Weaned Calves Grazing Ryegrass.

Annual cool-season grasses have increased concentrations of CP fraction A, readily degradable in the rumen, and supplementation with rumen undegradable protein may be a management practice to supply additional CP and improve performance of early weaned beef calves grazing cool-season grasses pastures. The objective of this study was to evaluate the effects of increasing levels of ruminally undegradable protein (RUP) supplementation on performance of early weaned (90 d of age) beef calves grazing annual ryegrass (Lolium multiflorum Lam.). The experiment was conducted at the Range Cattle Research and Education Center, Ona, FL from January to May 2007. Treatments were three levels of RUP supplementation, soybean meal (SBM, 35% RUP 65% RDP), SoyPLUS® (SP, modified expeller soybean meal with 60% RUP 40% RDP), and a 50:50 mixture of SBM-SoyPLUS® (SBMSP) supplemented at 0.15% BW, additional to a base supplement of 0.85% BW soybean hulls per head daily. Treatments were distributed in a randomized incomplete block design. Four early weaned beef calves, 2 steers and 2 heifers, were assigned in each experimental unit (0.3 ha). Calves were weighted in 28-d intervals. Herbage mass was measured every 14 d using a disk plate meter. Hand plucked samples were collected every 14 d and analyzed for CP and IVDOM. Significant variation in herbage mass, accumulation, IVDOM, and CP during the experimental period was observed but there was no difference among treatments. Average daily gain (0.69 kg), and live weight gain per hectare (1102 kg) did not differ among treatments. The increase of RUP supplementation levels did not improve performance of early weaned calves grazing annual cool-season pastures. Further studies with different RUP levels and sources are necessary to determine the potential benefits of this management practice to early weaned beef calves grazing annual cool-season pastures.