Effect of Roasting Raw Soybeans at Three Temperatures on In Situ Dry Matter and Nitrogen Disappearance in Dairy Cows

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Abstract
Solvent-extracted soybean meal, raw soybeans, and roasted raw soybeans were compared for chemical composition and in situ DMA and N rumen disappearance. Soybeans were drum-roasted to attain seed temperatures of 125, 150, and 165.degree. C; rolled; and cooled rapidly. In situ disappearance was measured by nylon bags (41-.mu.m pore size) in three ruminally cannulated lactating Holstein cows. Raw soybeans were affected chemically and physically by roasting. Roasting and rolling of raw soybeans diminished souble N by over 50%, visibly scorched the seeds, lowered the NDF content, and had no effect on ruminal DM and N disappearance rates, but significantly decreased the rapidly soluble "a" fraction and effective degradability of N. Soyhull loss probably occurred during flame roasting and rolling, hence the lower NDF in roasted beans. However, soybean meal was lowest in effective degradability of DM and N. Effective degradability of DM and N were not affected by temperature of roasting. Inadequate heat penetration of soy seeds from roasting probably occurred from the initial use of whole versus broken seeds and the short (45 to 60 s) roasting time and rapid cooling thereafter. Methods to physically rupture raw beans before roasting and maintain bean temperature after roasting should be explored.