Oral-stomach sampling as an alternative to rumen canula for the inoculation of in vitro batch fermentation systems

Abstract

The standard method to collect rumen fluid (RF) serving as inoculum for in vitro rumen fermentation assays and using ruminally cannulated animals is less and less accepted in some countries, and oral-stomach sampling (OSS) could be an alternative that needs to be validated. The objective of this study was to compare the in vitro rumen fermentation parameters of a large set of substrates with contrasted fermentation profiles using inocula obtained by OSS and from different sampling sites in the rumen of cannulated dairy cows. Rumen fermentation assays were conducted using twelve different substrates (six forages and six total mixed rations) and three types of inoculum consisting in fresh RF sampled in the reticulum (RF_ret), sampled both in the reticulum and the ventral sac (RF_mix) and using OSS (RF_tub) during three feeding periods creating variability in RF composition (control and acidogenic diets). There was a strong effect of substrate on all the parameters (P < 0.001) and a limited effect of the type of RF on the overall fermentability of substrates, particularly between RF_mix (standard method) and RF_tub that had similar values for dry matter (DM) and fiber degradabilities, gas production (including proportion of methane (CH₄) in the gas produced), total volatile fatty acids (VFA) and ammonia (NH₃). Above all, we did not detect any interaction between the substrate and the type of RF, highlighting the possibility to measure confidently relative differences among substrates or treatments. Overall, our results showed that fresh OSS can be a relevant alternative to the fresh RF sampling using cannulated animals. To keep OSS as a research tool on the long term, efforts should be continued to improve the standardization and the refinement of the OSS method.