Trusted information & resources for animal nutrition.

Technical Resources

Precise nutrition: Regression equations using KOH protein solubility to estimate digestible lysine and digestible arginine in commercial lots of soybean meal that have undergone the Maillard reaction

Ruiz, N., C. Parsons and B. Parsons

The objective of this study was to deliver a set of statistically significant regression equations (RE) for lysine (LYS) & arginine (ARG) that will allow poultry nutritionists & formulators to estimate the amino acid digestibility (AAD) of these amino acids (AAs) using a newly standardized protocol for the KOH protein solubility (KOHPS) test applied to commercial lots of soybean meal (CSBM). A total of 88 samples from a set of 100 previously analyzed for in vivo AAD and kept in frozen storage were analyzed for KOHPS. KOHPS values ranged from 86% to 13% while digestible LYS (DLYS) coefficients (COEFF) ranged from 0.96 to 0.47. Digestible ARG (DARG) COEFF ranged from 0.97 to 0.62. Because it became evident from the total LYS & total ARG analyses of the original samples that a net destruction of LYS & ARG occurred as KOHPS dropped. Therefore, previously published RE for total AAs regressed on protein content were used to calculate destruction-corrected LYS & ARG contents. Regressions of digestible COEFF on KOHPS were then run with & without corrected digestible COEFF for both AAs. Linear regression provided the best fit for KOHPS vs. corrected digestible COEFF for both LYS & ARG. One-slope broken line regression for LYS indicated that convergence criterion was met at KOHPS=80% & DLYS coefficient=0.88 meaning that an adequately processed CSBM lot by solvent extraction is optimum at a minimum of 80% KOHPS which in turn is correlated with a minimum in vivo DLYS of 0.88. Having a statistically significant RE between KOHPS & DLYS COEFF for CSBM contributes to the realization of precision nutrition. The data confirmed a long time observation that ARG is more digestible than LYS in CSBM, therefore by setting the minimum of 80% KOHPS for CSBM without Maillard reaction damage (overprocessing) on the basis of DLYS both AAs are at high AAD provided trypsin inhibitors are not in excess (underprocessing).

In conclusion, the RE here reported are the following:
DLYS (coefficient*100) = 0.59 * KOHPS + 41.06 (N=76; R-square=0.95; r=0.97; P <0.0001) DARG (coefficient*100) = 0.36*KOHPS + 62.33 (N=76; R-square=0.87; r=0.93; P < 0.0001)
NOTE: the utilization of these RE implies that the KOHPS values for CSBM have been generated using the newly standardized protocol.