Can dispersion methods affect the in vitro ruminal evaluation of substrates with different fermentabilities?

ABSTRACT The objective of this study was to evaluate the in vitro fermentation products, digestibility, gas production (GP) kinetics, and enteric greenhouse emissions (CH4 and CO2) of substrates with different forage:concentrate ratios (100F, grass hay only; 100C, concentrate mixture only, and mixture, an equal proportion of them) within non-woven fabric (NWT; 100 g/m2) or F57 (Ankom®) filter bags compared to directly dispersed in the medium (DIS), arranged in a 3 × 3 factorial arrangement. Substrates (0.5 g) were incubated using an AnkomRF GP System. Gas samples were collected during 24 and 48 h of incubation. We observed substrate × dispersion method interactions on GP at 48 h (GP48) and on in vitro organic matter digestibility (IVOMD). The GP48 and IVOMD of the 100C substrate were greatest in DIS, intermediate in NWT, and least in F57. With mixture substrate, there were no differences in GP48 and IVOMD between DIS and NWT, but they were greater than in F57. The GP48 and IVOMD were greater in NWT than in DIS and F57 when 100F was incubated. There were no dispersion method × substrate interactions on molar proportions and total volatile fatty acids. With the increase in forage:concentrate ratio incubated, there was a linear decrease in CH4 and CO2 emission relative to organic matter digested. Overall, CH4 and CO2 emissions and digestibility were lower when substrates were incubated within filter bags. The noteworthy interaction between the incubation method and substrates indicates that the ranking of these variables for substrates with differing fermentabilities changes with the dispersion method employed.