Total gas production per g of apparent DM disappearance (aDMD, after 72 h) in hay exhibited a quadratic pattern, being lower (p < 0.01) for grass harvested after 84 and 112 d of regrowth and higher (p < 0.01) for that harvested after 56 and 140 d.
Grass maturity did not affect (p > 0.10) aDMD or NDFD of hay, but these parameters were negatively affected (p < 0.01) when the grass was ensiled (Table 5).
Gas production [g.sup.-1] of aDMD, Admd, and NDFD were higher (p < 0.05) in grass hay as compared to silage (Table 5).
The higher aDMD (after 72 h) and NDFD for the silage made with grass after 112 d of regrowth may be explained by an improvement in the fermentation process as reflected by the higher level of lactate in this silage.
A higher level aDMD (after 72 h), NDFD and total VFA with hay compared to silage in this study was expected due to the consumption of easily fermented carbohydrates (WSC and hemicellulose) during the ensiling process.
In vitro ruminal fermentation products were calculated on a per g ADMD basis.
No interactive effect of particle size x surfactant level on ADMD, SD or on productions of total gas, methane gas and VFA was observed during the 24-h incubation.
Apparent DMD, SD and amount of total gas production per g of ADMD were all lower (p<0.01) for P2 than for P1 at 4, 12 and 24-h incubation (Table 5).
The linear increase of ADMD and SD as the concentration of the surfactant increased indicated that surfactant increased the microbial digestion of the barley grain.