Effect of heat damage and assay methodology on digestibility and bioavailability of amino acids in cottonseed and soybean meals

Experiments were conducted to evaluate the effect of assay methodology and heat damage on amino acid (AA) bioavailability for chick growth. Performance of chicks fed corn-cottonseed meal (CSM) diets formulated on a total AA basis was inferior to performance of chicks fed a corn-soybean meal (SBM) diet. Further evaluation showed that the true digestibilities of AA in CSM were lower than those in SBM. Consequently, growth performance of chicks fed up to 20% CSM on a digestible AA basis was found to be equivalent to that of chicks fed the corn-SBM diet. However, dietary levels of 30 or 40% CSM depressed performance even on a digestible AA basis.Further experiments were then conducted to determine if the true digestible lysine (Lys) and valine (Val) in CSM and SBM determined using the precision-fed cecectomized rooster assay were completely bioavailable for protein synthesis by chicks. Multiple regression slope-ratio analysis of chick growth assays indicated that the bioavailability of the digestible Lys in CSM and the digestible Lys and Val in SBM did not differ (P $>$.05) from 100%. Bioavailability of the digestible Val in CSM was lower and ranged from 78 to 96% depending on response parameter. However, these bioavailability values were still higher than those for crystalline Lys or Val when fed as part of an AA mixture simulating the digestible AA composition of CSM. The results indicated that the digestible Lys and Val in SBM and CSM as measured by the precision-fed cecectomized rooster assay are totally or almost totally bioavailable for protein synthesis.In the last study, SBM was autoclaved in the absence or presence of dextrose (SBM:dextrose ratio = 3:1) and true digestibility of Lys was compared to bioavailability of Lys. The digestible lysine in unautoclaved SBM was 100% bioavailable. For autoclaved SBM and autoclaved SBM-dextrose, bioavailability estimates for the digestible Lys were lower and varied among treatments, ranging from 55 to 87% for most response criteria. These results indicated that the digestible Lys in severely heat-damaged SBM measured by the precision-fed cecectomized rooster assay was not totally bioavailable for protein synthesis.U of I OnlyETDs are only available to UIUC Users without author permissio