Rumen‐Undegradable Protein Supplementation Effects on Early Weaned Calves Grazing Annual Ryegrass

Abstract

Early weaned beef calves (Bos spp.) can be raised on cool‐season pastures in Florida but more information on protein supplementation is necessary to optimize the performance of those calves. The objective of this study was to evaluate the effects of three levels of rumen‐undegradable protein (RUP) supplementation on performance of early weaned calves grazing annual ryegrass (Lolium multiflorum Lam.) pastures. The study was conducted in Ona, FL in 2007 and 2008. Treatments were 1.5 g kg−1 body weight (BW) supplementation of three levels of supplemental RUP, soybean meal (SBM, 350 g kg−1 RUP), Soyplus (SP, 600 g kg−1 RUP, modified expeller soybean meal, West Central, Ralston, IA), or a 50:50 mixture of soybean meal‐Soyplus (SBMSP, 475 g kg−1 RUP). Pasture size was 0.3 ha and four early weaned calves were assigned to each pasture. There was a linear increase in herbage mass (HM, from 1.9–2.1 Mg ha−1) and herbage allowance (HA, from 1.1–1.4 kg dry matter [DM] kg−1 live weight, LW) with increasing levels of RUP. Increased RUP supplementation decreased forage dry matter intake (FDMI) and total dry matter intake (TDMI) in 2008 but there was no effect in 2007. There was no difference in average daily gain (ADG, 0.76 kg d−1) among treatments. Increasing the levels of RUP supplementation has potential to increase stocking rates of early weaned calves grazing annual ryegrass pastures.

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

“…Supplementation may alter grazing behavior and forage intake, which affects forage growth and appearance of new tissues with greater nutritive value. Vendramini et al (2011) observed that annual ryegrass pastures grazed by early weaned calves receiving greater levels of RUP had greater HM and HA. The greater HM and HA observed was attributed to decreased FDMI of the calves receiving greater RUP supplementation levels.…”

“…In contrast, the replacement of sources of RDP by RUP may cause a depression of 7% on passage of microbial protein to the small intestine and the SBMSP treatment may have supplied a balanced amount of nonammonia nonmicrobial N and microbial protein. Vendramini et al (2011) tested the effects of increasing levels of RUP on FDMI, TDMI, and ADMD of calves receiving annual ryegrass. In the first year of the trial, there was no effect of the treatments on FDMI, TDMI, and ADMD; however, there was a significant decrease in FDMI and TDMI in the second year.…”

“…Early weaned calves were Angus-sired (crossbred cows sired by Angus bulls) products of primiparous cows. Before this experiment, the calves were weaned on 3 Jan. 2007 and 10 Jan. 2009 at approximately 90 d of age and grazed annual ryegrass from January to April (Vendramini et al, 2011). Calves received the same supplement treatments in winter and summer.…”