Effects of supplemental energy source and amount on forage intake and performance by steers and intake and diet digestibility by sheep.

Abstract

Two levels of concentrate supplements containing different types of carbohydrates (corn-soybean meal, CSBM; wheat middlings, WM; and soybean hulls, SBH) were evaluated for effects on forage intake and performance in growing steers and total diet digestibility in sheep. In Exp. 1, 63 crossbred yearling cattle (298 and 377 kg initial BW for yr 1 and 2, respectively) were given ad libitum access to chopped bermudagrass (Cynodon dactylon [L.]) hay with no supplementation (CONTROL) or with 25 or 50% of projected total TDN intake from CSBM, WM, or SBH. In Exp. 2, digestibilities of organic matter (OMD) and neutral detergent fiber (NDFD) were determined with sheep fed levels of hay and concentrates similar to those used in the growth trials. Hay intake was 1.99% of BW for steers fed hay alone and averaged 1.93% of BW in steers fed supplements at the low level. At the high level of concentrate supplementation, hay intake was depressed (P < .001) to a similar extent (1.63% of BW) in steers supplemented with CSBM, WM, or SBH. AT the low concentrate level, shrunk ADG was similar (.63 kg/d) among supplements, but at the high concentrate level steers fed SBH had higher (P = .06) shrunk ADG (.95 kg/d) than steers fed CSBM (.76 kg/d). Body condition score (BCS) increased more (P = .06) for CSBM- and SBH- than for WM-supplemented steers. Total tract OMD was lower (P < .001) in sheep fed WM (54.8% for low and 56.9% for high supplementation levels) than in sheep fed CSBM (57.4 and 62.6%) or SBH (57.2 and 62.5%). Total tract NDFD was higher (P < .001) for the SBH (58.9% for low and 63.3% for high levels) diets than for CSBM (54.6 and 51.0%) or WM (54.6 and 51.8%) diets. Supplements containing highly digestible fiber (SBH) produced less negative associative effects than high-starch supplements (CSBM) when fed with bermudagrass hay at the high level (.8 to 1% of BW), but no differences were found at the low feeding level (.4 to .5% of BW).