Impacts of herbage distribution, botanical composition, and rumen inoculum source on in vitro fermentation kinetics

The random sourcing of rumen liquor from abattoir-slaughtered cattle may influence in vitro gas production results due to variations in diet composition. This study evaluated the effects of herbage distribution, botanical composition, and rumen liquor source on rumen in vitro fermentation kinetics. Three districts in Uganda's cattle corridor with diverse grazing systems and vegetation types were purposively selected: Mbarara (improved mixed pastures), Nakasongola (woody shrublands), and Napak (grasslands). Karamoja had the highest herbage diversity (n = 40), followed by Mbarara (n = 32) and Nakasongola (n = 19), with grasses comprising over 75% of samples from Nakasongola and Mbarara, and 53% from Karamoja. Karamoja herbage exhibited significantly higher crude protein (132.6 g/kg DM). Gas production varied (P < 0.001) across herbage sources during incubation. Fermentation kinetics were influenced by both the rumen liquor and herbage source (P < 0.001), while gas production rate from the insoluble fraction (b) was only affected by herbage source (P < 0.001). In vitro organic matter digestibility (IVOMD), metabolizable energy, and short-chain fatty acids were also significantly influenced by herbage source. Herbage composition had a greater impact on fermentation kinetics and IVOMD than the source of rumen liquor. These results suggest that rumen liquor from cattle raised under similar grazing systems yields consistent in vitro gas production results. Consequently, these results demonstrate that rumen fluid can be sourced from animals slaughtered in abattoirs if precaution is taken to use rumen fluid from animals on a comparable diet.