In vitro fermentation kinetics of carbohydrate fractions of fresh forage, silage and hay of Avena sativa

The objective of this experiment was to evaluate the influence of preservation methods on the fermentation kinetics of carbohydrate fractions of fresh forage, hay and silage of oats, which have been harvested at the milky stage of grain ripening. Samples of unfractionated forage (WF), residue insoluble in 90% ethanol (EIR) and isolated neutral detergent fibre (NDF) were fermented in vitro and the gas production was monitored. To obtain the gas production and fermentation kinetics of the ethanol-soluble fraction (A fraction) the gas produced from the EIR fermentation was subtracted from the WF gas at each time point. The same approach was used to obtain the gas production and fermentation kinetics of the fraction insoluble in 90% ethanol but soluble in neutral detergent solution (B1 fraction), by subtracting the isolated NDF gas curve from the corresponding EIR curve. The fractional maximum rate of gas production (RM) was lower for both preserved forages (p < 0.01 for silage; p < 0.05 for hay) than for fresh forage. Ensiling did not change the size of the A fraction but reduced by 40% its RM (p < 0.01) compared with fresh forage. The potential gas production from the B1 fraction and its RM were reduced by 19% (p < 0.01) and 44% (p < 0.05), respectively. RM of both A and B1 fractions was the same for hay and fresh forage. The curve subtraction technique may be used to obtain an estimation of the rate for neutral detergent-soluble fractions and to determine changes due to ensiling and haymaking on the rate of gas produced