Excessive heat during processing can reduce the concentration and bioavailability of Lys in soybean ingredients via Maillard reactions, lowering growth performance in weanling pigs. Reactive Lys (the Lys not bound in Maillard products) is the relevant bioavailable part of Lys that can be used for protein synthesis by the animals. We tested the hypothesis that: (1) growth performance can be predicted from reactive Lys supplied by heat-damaged soybean ingredients, and (2) crystalline amino acids (AA) can be added to the diet to compensate for heat-induced losses.