In situ and in vitro techniques for estimating degradation parameters and digestibility of diets based on maize or sorghum

An experiment was conducted to evaluate: (1) the effects of ensiling maize or sorghum grains after reconstitution on readily soluble fraction (a), potentially degradable fraction in the rumen (b) and rate constant for degradation ofb(c) of dry matter (DM), organic matter (OM) and starch (STA); and (2) an appropriate incubation time forin situorin vitroprocedures to estimatein vivodigestibility. Four rumen-cannulated Nellore bulls (body weight = 262 +/- 19.6 kg) distributed in a 4 x 4 Latin square were used. Diets were based on dry ground maize (DGM); or dry ground sorghum (DGS); or reconstituted ground maize silage; or reconstituted ground sorghum silage.In vitroandin situincubations of the individual grains and diets were simultaneously performed within vivodigestibility. In general, reconstituted grains and diets based on reconstituted grains presented greater (P< 0.05) fractionaand lower (P< 0.05) fractionbof DM, OM and STA compared to dry grains and diets based on dry grain. However, the magnitude of response of the reconstitution and ensiling process on DM and OM degradability parameter was greater for maize than that for sorghum. Moreover, no differences (P> 0.05) were observed between DGM- and DGS-based diets forcestimates. The results suggest that the reconstitution process promotes grains protein matrix breakdown increasing STA availability. The incubation times required forin vivodigestibility estimations of DM, OM and STA are 24 h forin situand 36 h forin vitroprocedures.