ADDITIVITY OF APPARENT AND TRUE ILEAL AMINO-ACID DIGESTIBILITIES IN SOYBEAN-MEAL, SUNFLOWER MEAL, AND MEAT AND BONE MEAL FOR BROILERS

An experiment was conducted to determine the additivity of apparent an d true ileal amino acid digestibility values in soybean meal (SBM), su nflower meal (SFM), and meat and bone meal (MBM). A total of 63 indivi dually caged 5-wk-old broilers were assigned to seven groups and given semi-purified diets containing SBM, SFM, MBM, and their combinations. True digestibilities were estimated by using the homoarginine in guan idinated proteins as the marker. Additivity was tested by comparing th e differences between the observed digestibilities of ingredient combi nations and the predicted values from measurements with individual ing redients. In general, for both apparent and true digestibilities, ther e were no significant differences (P > 0.05) between the observed and predicted values in ingredient combinations. The only exception was SB M + MBM combination, in which the observed values for apparent digesti bilities of aspartic acid, serine, glutamic acid, isoleucine, and tyro sine were significantly higher (P < 0.05) than the predicted values. O verall, the present results indicate that amino acid digestiblity valu es are additive and that digestible amino acid supply in a complete di et can be predicted from amino acid digestibilities of individual ingr edients.