Oligosaccharides, onion peel, and essential oils as feed additives in the diet of dairy cattle: in vitro fermentation, greenhouse gases, ruminal nutrient degradability, and volatile fatty acid production

This study investigated the effect of inclusion of dietary oligosaccharides, onion peel, and an essential oil blend (EOB; containing anise, clove, oregano, cedarwood, and ginger in the ratio 4:2:2:1:1) individually and in combinations in the total mixed ration of dairy cattle on in vitro gas production (GP), dry matter disappearance (DMD), fiber fraction disappearance, and total and individual volatile fatty acid (VFA) production. EOB was used at 200 mu L g(-1) of feed while the other additives were administered at 3% of the feed on a dry matter basis. The in vitro batch culture technique was used for this experiment and the design was a completely randomized design with 12 treatments replicated eight times. The total GP at 24 h was significantly (p < 0.0001) reduced by the inclusion of EOB-containing additives in the total mixed ration. The lowest gas volume was recorded for the treatment containing mannanoligosaccharide + EOB while the highest value was recorded for sole onion peel treatment. The EOB treatment had the lowest methane production while onion peel alone had the highest values for the greenhouse gas parameters. The inclusion of EOB individually and in combination with the oligosaccharides reduced (p < 0.05) propionate and increased acetate molar proportions, with the highest acetate and lowest propionate noted for the galacto-oligosaccharide and onion peel mixture treatment. Inclusion of the additives evaluated in this study had positive effects on rumen fermentation and digestibility indices with a potential for abatement of greenhouse gases when EOB is present individually or in combination with the oligosaccharides.