EFFECT OF ROASTING ON SITE AND EXTENT OF DIGESTION OF SOYBEAN-MEAL BYSHEEP .1. DIGESTION OF NITROGEN AND AMINO-ACIDS

Six mature wethers (BW 72 kg) with ruminal, duodenal, and ileal cannul as were fed a control (no added soybean meal [SBM]) diet or diets cont aining unheated SBM or SBM roasted at 165 degrees C for 75, 150, 180, or 210 min in a 6 x 6 Latin square experiment. Concentrations of indic ators of heat exposure (ADIN, ADF, NDF) in SBM increased with increasi ng roasting time. Duodenal flows of total N, non-bacterial N, and SBM N increased (P <.05) linearly with increased roasting time. Small inte stinal (SI) digestibility (percentage entering SI) of total N and SBM N was influenced quadratically (P <.05) by roasting time; SI digestibi lities were modestly increased by heating SBM to 150 min, then decline d dramatically when SBM was heated for 180 and 210 min. These response s resulted in a quadratic (P <.05) increase in quantity of total and S BM N disappearing in the SI; quantities increased as SBM was heated to 150 min and remained unchanged when SBM was heated for 180 and 210 mi n. These responses resulted in a quadratic (P <.05) increase in quanti ty of total and SBM N disappearing in the SI; quantities increased as SBM was heated to 150 min and remained unchanged when SBM was heated f or 180 and 210 min. Duodenal flows and SI digestibilities of total and non-bacterial amino acids (AA) and of most individual AA followed pat terns similar to those observed for N. Maximum quantities of total and individual AA disappeared from the SI when wethers were fed SBM roast ed at 165 degrees C for 150 min. Evaluation of the effects of heat tre atment on the nutritive value of a protein source for ruminants should include considerations for both ruminal protein escape and SI availab ility of escaped protein and for the nature of the AA supply absorbed from the SI.