The study comprised two samples of solvent-extracted soybean meal (SBM) and two samples of xylose-treated SBM (SoyPass(R)). The main objectives were to determine effective rumen degradability (ERD) and intestinal indigestibility of their individual amino acids (AA) in situ. The relative contribution of Lys was on average 17% lower and of Arg 7% lower in SoyPass(R); than in SBM (p < 0.05). Manufacturing of SoyPass(R) increased significantly the relative contribution of Ile, Leu, Val and Gly, but these effects were small in magnitude. Effective rumen degradabilities of total AA (TAA) calculated at a rumen outflow rate of 8% h(-1), was as low as 29% for SoyPass(R) compared to 53% for SBM. The corresponding values for crude protein (CP) were 27 and 52% for SoyPass(R) and SBM, respectively. In SBM, Arg, Glu and Lys had higher (p < 0.05) ERD than TAA, whereas Ser, Phe, Leu, Gly, Thr, Tyr, Ile, Cys, Val, Ala and Met showed lower (p < 0.05) ERD than TAA. In SoyPass(R), ERD of Lys and Cys did not differ significantly from TAA. With these exceptions, variation in ERD among AA in SoyPass(R) was as in SBM. However, the differences between individual AA and TAA were much smaller than in SBM. Intestinal indigestibility of TAA measured on original feed (OF) was 1.8 and 2.0% for SBM and SoyPass(R), respectively (p > 0.05). For CP, the corresponding values were 2.0% for SBM and 2.3% for SoyPass(R). Pre-incubating the samples in the rumen for 16 h, numerically decreased intestinal indigestibilities of all individual AA, but the effect was significant for only 5 AA. There were significant differences in intestinal indigestibilities among AA, but the differences were small in magnitude. From the results obtained, it was concluded that, for SBM and SoyPass(R), TAA in the protein fraction digested in the intestine (PDI) can be predicted accurately by using proportion AA-N: N in rumen undegraded protein (RUP) of 0.85, and ERD and intestinal indigestibility as for CP. For SoyPass(R), this way of prediction of individual AA would result in only small err-ors, at least for those AA which are regarded as limiting in milk production. In contrast, for SBM satisfactory prediction of individual AA absorbed in the intestine requires determination of ERD on individual basis. (C) 2000 Elsevier Science B.V. All rights reserved.
