Effects of Increasing Rumen‐Undegradable Protein Supplementation Levels on Early Weaned Calves Grazing Stargrass

Abstract

Early weaned beef calves (Bos spp.) grazing warm‐season grasses may benefit from increasing levels of rumen‐undegradable protein (RUP) supplementation due to the limited RUP supplied by the forage and their high nutrient requirements. The objective of this study was to test the effects of increasing levels of RUP supplementation on performance of early weaned calves grazing stargrass (Cynodon nlemfuensis Vanderyst) pastures. The experiment was conducted in Ona, FL, from May to August 2007 and 2008. Treatments were 1.5 g kg−1 body weight (BW) of three levels of supplemental RUP from soybean [Glycine max (L.) Merr.] meal (SBM) (350 g kg−1 RUP), Soyplus (SP) (600 g kg−1 RUP) (a modified expeller SBM) (West Central, Ralston, IA), or a 50:50 mixture of SBM and Soyplus (SBMSP) (475 g kg−1 RUP). Pasture size was 0.51 ha and four early weaned calves were assigned to each pasture. There was no effect of the treatments on mean herbage mass (HM; 2.7 Mg ha−1), forage crude protein (CP) (171 g kg−1), in vitro digestible organic matter (IVDOM) concentration (640 g kg−1), or calf average daily gain (0.56 kg d−1). Increased RUP supplementation did not affect forage dry matter intake (mean = 2.0% BW); however, there was a linear decrease in apparent dry matter digestibility from 640 to 600 g kg−1. Increasing levels of RUP supplementation may not increase performance of early weaned calves grazing stargrass pastures when forage CP is not limiting.