Lipid-induced depression of methane production and digestibility in the artificial rumen system (RUSITEC)

An artificial rumen (RUSITEC) equipped with eight fermenters was used to examine the effects of canola oil (CA), cod liver oil (CD) and coconut oil (GO) on methane production, dietary digestibility and rumen microbial populations. The experiment, repeated three times, involved two diets (100% grass hay or a 90%:10% wheat:hay mixture) either untreated (controls) or sprayed with CA, CD or CO (10%, wt/wt) in a 2 x 4 factorial arrangement. Dry matter disappearance and CH4 production were greater (P < 0.05) from untreated concentrate diet than from untreated hay. There were significant interactions (P < 0.05) between diet and lipid type for DM digestion and several of the fermentation parameters. Coconut oil decreased (P < 0.05) DM and neutral detergent fibre disappearance of hay but did not affect digestion of concentrate. All oils, especially CO, depressed (P < 0.05) CH4 production (mmol gl digestible DM) and methanogenic populations regardless of diet. Methanogens on GO-treated diets numbered less than 1% of those on CA- and CD-treated diets. Total viable, amylolytic, and cellulolytic bacterial numbers were also substantially reduced (P < 0.05) by CO, but not by CA or CD for both diets. Bacterial colonization and digestion of GO-treated hay was markedly less extensive than that observed on untreated, CA- or CD-treated hay. The molar proportion of propionate produced was increased (P < 0.05) by CA and CD, for the hay diet, but not for the concentrate diet. Coconut oil decreased (P < 0.05) the molar proportion of propionate produced on the hay diet and increased (P < 0.05) it on the concentrate diet. Of the three oils, CO was most inhibitory to CH4 production and depressed fibre digestion. The CA and CD also decreased CH4 production, but did not affect feed digestion in either diet. Consequently, the amount of metabolizable energy of feeds may be increased when diets are supplemented with these oils.