In dairy cattle, the stomach tube method is not a feasible alternative to the rumen cannulation method to examine in vitro gas and methane production

Abstract

The objectives were to compare in vitro gas and methane (CH4) production kinetics using rumen fluid as inoculum collected via the rumen cannulation (CAN) method and with the oral stomach tube (OST) method, and to test for interactions between the type of inoculum and the diet fed to the donor cows as well as with the substrate incubated. Four rumen-cannulated lactating Holstein-Friesian cows (364 ± 20 days in milk, 690 ± 37 kg of bodyweight, 22.0 ± 6.0 kg of milk/day; mean ± SD) were blocked in pairs balanced over treatment sequence in a 2 × 2 crossover design. Cows were fed a total mixed ration consisting of 40% maize silage, 30% grass silage, and 30% concentrate on dry matter (DM) basis, with or without dietary linseed oil (a difference of 23 g/kg DM in fat content between the two diets). Rumen fluid was collected using the CAN and the OST method from each cow at d 17 of each experimental period. Subsequently, a 48 h gas production (GP) experiment was performed in which rumen fluid from each donor cow × rumen fluid sampling method was incubated with three substrates, viz. amygold, lupine, and wheat. The pH of the rumen fluid obtained using the OST method was higher than that of the rumen fluid obtained using the CAN method, whereas the total VFA concentration was lower and the VFA molar proportions unaffected. Multiple diet × inoculum and substrate × inoculum interactions in in vitro GP and CH4 kinetic parameters were observed. Furthermore, several GP and CH4 kinetic parameters, including total GP, absolute, asymptotic, and relative CH4 production, and maximum CH4 production rate, were higher for the CAN method compared with the OST method. The opposite was observed for, amongst others, the switching characteristic of the CH4 production profile and the half time to reach maximum asymptotic GP of the insoluble fraction. In conclusion, rumen fluid obtained using the OST sampling technique differs from that obtained using the CAN method, resulting in differences in in vitro gas and CH4 production profiles between both methods. The multiple interactions indicate that the rumen fluid sampling method can affect the in vitro GP and CH4 kinetics found for diet and for substrate. The results of this study therefore do not support the OST method as a feasible alternative to the CAN method in dairy cattle to examine in vitro gas and CH4 production.