Effect of Roasting Temperature on the Proportion of Soybean Meal Nitrogen Escaping Degradation in the Rumen

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Abstract
Ruminal- and duodenal-cannulated steers were used in a 5 × 5 Latin-square design to determine the effect of roasting temperature on the proportion of soybean meal (SBM) N escaping degradation in the rumen. Dehulled SBM was roasted to three temperatures (115, 130 or 145 C) and compared to nonroasted SBM. A urea basal diet was used to measure the flow of endogenous, protozoal and basal plant N. Lanthanum, chromium-ethylenediaminetetracetic acid (Cr-EDTA) and diaminopimelic acid (DAPA) were used as particulate, liquid and bacterial markers, respectively. Roasting temperature had a linear (P<.05) effect on the amount of SBM-N escaping ruminal degradation. Percentage SBM-N escaping degradation was: 14.7, 29.7, 36.2 and 47.3 for non-roasted, 115, 130 and 145 C SBM, respectively. Duodenal flow rates of particulate and liquid digesta were not influenced (P>.05) by source of supplemental N. Bacterial N flow and efficiency of bacterial protein synthesis were similar (P>.05) for all diets. Rate of in situ N disappearance was reduced (P<.05) by roasting. Nonroasted, 115, 130 and 145 C SBM had rates of in situ degradation of 11.3, 4.3, 4.1 and 1.9%/h, respectively. Acid detergent insoluble N (ADIN) and acid pepsin insoluble N (APIN) were increased threefold by roasting to 145 C, which was reflected in increased (P<.05) duodenal flow of ADIN in steers fed 145 C SBM. Roasting to 115 or 130 C did not influence (P<.05) duodenal flow of ADIN or ADIN content of SBM. Nitrogen soluble in McDougall's artificial saliva increased (P<.01) linearly as pH increased from 5.5 to 7. Roasting temperature had a quadratic effect (P<.01) on soluble N. Roasting can be used to increase the ruminal escape of SBM-N without significantly increasing APIN. Copyright © 1985. American Society of Animal Science . Copyright 1985 by American Society of Animal Science.