Soybean hulls as a primary ingredient in forage-free diets for limit-fed growing cattle

In Exp. 1,300 heifers (260 kg initial BW) were used to compare growth perfo rmance of cattle fed forage-free diets containing predominantly soybean hul ls with that of cattle receiving roughage- and corn-based diets and to dete rmine whether cattle fed soybean hull-based diets would respond to suppleme ntation with methionine hydroxy analogue (MHA), lipid-coated be taine, or c oncentrated separator by-product (CSB; a source of betaine). Treatments inc luded 1) a roughage-based diet fed at 2.75% of BW, 2) a corn-based diet fed at 1.5% of BW, 3) a corn-based diet fed at 2.25% of BW, 4) a soybean hull- based diet fed at 1.5% of BW (SH1.5), 5) a soybean hull-based diet fed at 2 .25% of BW (SH2.25), 6) SH1.5 top-dressed with 11.4 g/d Alimet (10 g/d MHA) , 7) SH2.25 top-dressed with 11.4 g/d Alimet, 8) SH2.25 top-dressed with 7 g/d of a lipid-coated betaine product (4.2 gld betaine), and 9) SH2.25 top- dressed with 250 g/d CSB (15.5 g/d betaine). Supplemental MHA, betaine, and CSB did not change DMI, ADG, or gain:feed ratio for cattle fed soybean hul ls. Heifers fed soybean hull-based diets gained 29% slower (P < 0.05) and h ad 27% lower gain:feed ratios than heifers fed the corn-based diets. Cattle fed soybean hull-based diets had gains that were lower (P < 0.05) than tho se of cattle fed the roughage-based diets, but gain:feed ratios were simila r because cattle were fed less of the soybean hull-based diets. Roughage-fe d cattle had similar gains but 25% lower (P < 0.05) gain:feed ratios than c attle fed the corn-based diets. In Exp. 2, degradation by ruminal microbes of betaine in anhydrous betaine, betaine-HCl, feed-grade betaine, lipid-coa ted betaine, and CSB was evaluated in vitro using ruminal inocula collected from steers fed a high-grain or high-roughage diet. The roughage diet led to less betaine disappearance than the grain diet. More betaine was degrade d from CSB than from other sources, perhaps because sugars provided by CSB stimulated fermentation, but no large differences occurred among the other four sources. Betaine from all sources was extensively degraded, although s ome betaine may escape ruminal degradation.