Study of in vitro fermentation kinetics of herbage mass samples and simulated grazing samples for dairy cows

Abstract

An experiment to study the characteristics of in vitro fermentation of forage was carried out in herbage mass samples (FD) and simulated grazing samples (FA), at two sward heights of a permanent pasture. The digestion kinetics of the forage was studied using in vitro gas production method. Data collected were fitted according to the equation of Orskov and McDonald. Gas production was greater (P<0.05) from herbage mass samples than simulated grazing samples at 12, 21, and 27 hours of incubation (161.7 v/s 150.6, s.e.d.= 4.23; 217.6 v/s 209.2, s.e.d.= 3.65; and 242.1 v/s 234.7, s.e.d.= 3.34, respectively). However, after 27 hours of incubation, no significant effect (P>0.05) of type of sample, either on the amount of gas produced or on the kinetic of fermentation, were found. The dry matter disappearance after 96 hours of incubation was significantly lower (P<0.05) for herbage mass samples compared with simulated grazing samples (0.908 v/s 0.873, s.e.d.= 0.005), but with no effect of sward height (P>0.05). These findings show the benefits of complementing in vitro gas production measurements with post digestion residue determinations to improve the knowledge on the nutritive value of feed fermented in the rumen.