Effect of Roasting on Utilization of Soybean Meal by Ruminants

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Abstract
Commercially prepared, solvent-extracted, dehulled soybean meal (SBM) was roasted at five temperatures (102, 128, 144, 159 and 185 C). Roasting at 159 and 185 C increased (P<.05) the percentage N recovered as acid detergent insoluble N (ADIN). A chick bioassay was conducted in which roasted SBM replaced nonroasted SBM in a corn-soy diet formulated to contain approximately 75% of the total N from SBM. Daily gain, dry matter intake and gain/feed were similar (P>.05) for chicks fed nonroasted, 102, 128 and 144 C SBM. Chicks fed the 159 and 185 C SBM gained less, consumed less dry matter and had reduced gain/feed (P<.05) compared to chicks fed nonroasted SBM. The simple correlation coefficient between ADIN of SBM and daily chick gain was −.99 (P<.01). A N balance study, using young ram lambs in which diets containing approximately 33% of the total N as SBM were fed, suggested that apparent N digestibility, N absorption and retention were similar (P>.05) for lambs fed nonroasted, 102, 128, 144 and 159 C SBM. Roasting SBM at 185 C depressed (P<.05) apparent N digestibility and absorption but did not affect (P>.05) N retention in this study. Rumen ammonia levels were not altered (P>.05) by including roasted SBM in the diet but tended to be lower when roasted SBM was fed. An in situ dacron bag study was conducted to estimate the effect of roasting on the degradation of SBM in the rumen. Although the hour of incubation × SBM interaction was significant, in general, as roasting temperature increased, less N disappeared from the dacron bag, suggesting that roasting reduces the rate of SBM degradation in the rumen. Based on the chick bioassay and the dacron bag study, it appears that roasting SBM at 128 or 144 C may increase the amount of undegraded digestible SBM protein reaching the small intestine of the ruminant. Copyright © 1982. American Society of Animal Science . Copyright 1982 by American Society of Animal Science