In Vitro Estimation of Dry Matter and Crude Protein Digestibility

Abstract

A number of experiments were carried out to determine some of the parameters affecting the estimation of apparent digestibility of dry matter (DDM) and crude protein (DCP) by a two-stage, in vitro method, Experiments investigated the effects of pepsin concentration, time of incubation, pH, the effect of particle size on DDM and DCP, and the relationship between apparent in vivo and in vitro digestibility.Increasing the concentration of pepsin to 1140 units/10 ml .075N HCl in the first phase of incubation increased %DCP (P<.05), while %DDM increased significantly (P<.05) only to 580 pepsin units/10 ml .075N HCl solution. In the first stage of incubation with pepsin there was a significant (P<.05) increase in %DDM and %DCP in the second 1-hr period. In the second stage of incubation, involving porcine intestinal fluid, %DDM increased significantly (P<.05) in the first three 1-hr periods, while no significant (P<.05) increase in %DCP was observed after the second 1-hr period. In the second intestinal stage of incubation, there was no significant (P>.05) difference in %DDM for pH's 6.6 to 6.9. At pH 6.5 there was a significant (P<.05) decrease in %DDM. There was no significant (P>.05) effect of pH on %DCP.By reducing particle size of test material the accuracy of predicting apparent in vivo DDM and DCP was increased for all diets. The in vitro method gave a reliable estimation of apparent DDM and DCP in vivo. The correlations (r) between in vitro and in vivo estimates were high, .99 and .93 for %DDM and %DCP, respectively, when diets were ground to pass through a .4 mm screen. Prediction equations obtained from linear regression analysis were y = .901X + 7.214 and y = 1.331X −26.66 for DM and CP, respectively, where y = in vivo digestibility and X = in vitro digestibility.