Pepsin-Cellulase Digestibility of Pasture Silages: Effects of Pasture Type, Maturity Stage, and Variations in the Enzymatic Method

Abstract

Enzymatic in vitro digestibility has been studied as a method to predict energy values of forages for ruminants, although results have been affected by type of forage and methodological details of the technique. This work was performed to evaluate the effects of cellulase concentration (0.75, 1.0 and 6.25 g L -1 ), incubation time (24 or 48 h) and type of final washing of the residue (water or acetone) on the in vitro digestibility of the dry matter (DMD), organic matter (OMD) and content of digestible organic matter in the DM (D value) of silages made at three maturity stages from three types of pastures: a) permanent pasture (Dactylis glomerata, Lolium perenne, Bromus catharticus Vahl var. catharticus, Trifolium repens and Holcus lanatus); b) Italian ryegrass ley (Lolium multiflorum Lam. cv. Tama); c) oats (Avena sativa L.) and d) mixed pasture (L. perenne-T. repens). Regression equations among cellulase results and in vitro values obtained with rumen fluid were also developed. Higher enzyme concentration, longer incubation time and final washing with acetone, resulted in a significant (P < 0.05) increase in DMD, OMD and D value. A strong interaction (P < 0.001) among forage type, maturity stage and incubation time was observed. Interactions between stage and enzyme concentration were also apparent (P < 0.05) for D value, DMD and OMD. Type of pasture and maturity affected the performance of the enzymatic method to predict in vitro digestibility obtained with rumen fluid. Therefore, different prediction equations should be developed for any combination of the above mentioned factors. Adjusting this methodology with in vivo data is encouraged to improve prediction of digestibility values.