Precision and additivity of organic matter digestibility obtained via in vitro multi-enzymatic method

摘要

The enzymatic digestibility of organic matter(EDOM) method is an in vitro multi-enzymatic methodfor estimating the organic matter (OM) digestibilityof feeds. The EDOM method previously showed highaccuracy with in vivo values for compound feeds. Theaim of this study was to evaluate the precision of theEDOM method and determine its additivity, comparedwith the long-assumed additive property of the chemicalcomponents of compound feeds. 149 feed samples,70 commercial compound feeds and 79 associated ingredients,were analyzed in a laboratory (lab1) for OMdigestibility measured by EDOM (OMD_(EDOM)) with 2repetitions separated in time to estimate repeatability.Of the total samples, 49 compound feeds were furtheranalyzed in a commercial laboratory (lab2) for OMD_(EDOM)to determine reproducibility. The 49 compoundsand their 69 associated ingredients were also analyzedby lab2 for dry matter (DM), ash, crude protein (CP),neutral detergent fiber (NDF), and starch. The EDOMmethod resulted in an intralaboratory correlation of98.9% and an interlaboratory correlation of 92.6%,with no significant mean bias between the 2 laboratoriestested. The formulation of compound feeds, totalmixed rations, and mixtures in general assumes thattheir nutrient content can be calculated by addingtogether the nutrient supply of individual ingredients.This is of great importance in the feed industry for thecreation of compound feeds. Additivity of OMD_(EDOM)for the compound feed samples was evaluated by comparingthe sum of the digestible OM (DOMEDOM) ofthe ingredients (predicted) with DOMEDOM estimateddirectly in the compound feed (observed). The regressionof predicted versus observed showed a coefficientof determination (R2) of 0.93 and root mean squareerror (RMSE) of 1.07% of total DM, with no linearbias but with a mean bias (0.83% of DM). Additivity ofCP, starch, crude fat, and NDF showed an R2 of 0.95,0.98, 0.95, and 0.93, and RMSE of 1.56, 1.90, 0.39, and1.46% of DM, respectively, all presenting linear bias.Crude fat also presented mean bias. Although significant,all linear and mean bias for DOMEDOM and chemicalcomponents were within the acceptable error limitsfor declaration of feeds. The results demonstrate thehigh precision of the EDOM method and its additiveproperty, which is an advantage for the estimation ofOM digestibility in compound feeds. Moreover, resultsof the tests of chemical components confirm their additiveproperty.