Abstract
BACKGROUND: Accurate dosing of feed additives is often required to evaluate their effects on rumen fermentation. This can be done using soluble but nonfermentable hydroxypropyl methylcellulose (HPMC) hard capsules. OBJECTIVES: The aim of the study was to evaluate the effect of HPMC hard capsules on the extent and rate of in vitro gas production in eleven feeds. METHODS: Six high-fibre feeds and five concentrates, were weighed into syringes either directly or into HPMC capsules and incubated anaerobically in 30 mL buffered rumen fluid at 39°C. Data obtained from gas production measurements were fitted using the Gompertz model to obtain kinetic parameters for gas production. RESULTS: HPMC hard capsules had no effect on the gas production of the blank sample and concentrate feeds. In contrast, high-fibre feeds weighed in HPMC showed a significant decrease (p < 0.05) in total gas production and gas produced within 24 h of incubation. CONCLUSIONS: The use of HPMC hard capsules was found to be inappropriate for determining gas production kinetics because fermentation subsides at a certain point when peak fermentation is reached (at TMFR), resulting in a decrease in both total potential gas production and gas production within 24 h of incubation. This is particularly evident when high-fibre feeds are incubated.