Effects of Different Essential Oil Blends and Fumaric Acid on In Vitro Fermentation, Greenhouse Gases, Nutrient Degradability, and Total and Molar Proportions of Volatile Fatty Acid Production in a Total Mixed Ration for Dairy Cattle

The present study evaluated the inclusion of fumaric acid and essential oil blends (EOBs) containing anise, cedarwood, clove, cumin, eucalyptus, garlic, ginger, lavender, lemongrass, nutmeg, oregano, and peppermint at different proportions on in vitro dry matter (DM) disappearance (DMD), fiber fraction disappearance, the efficiency of microbial production, and the total volatile fatty acids (VFAs). Ten treatments without (control treatment) or with different EOB/fumaric combinations were used in the study with eight replicates. The EOB inclusion level was 200 μL/g of feed (total mixed ration, (TMR)) while fumaric acid was administered at 3% of the TMR (DM basis). The highest DMD, in vitro true degradable DM, partitioning factor (PF24), and in vitro apparent degradable DM were recorded for the fumaric only treatment and the control. Neutral detergent fiber disappearance was reduced with the inclusion of EOB/fumaric combinations. The production of microbial mass and undegraded DM were higher (p < 0.001) for all EOBs and EOB and fumaric treatments. The inclusion of EOB and fumaric combinations reduced (p < 0.001) the total gas production, methane, and ammonia, with a higher PF24 value noted for EOB3 treatment. The inclusion of individual EOB1 containing garlic, lemongrass, cumin, lavender, and nutmeg in a ratio of 4:2:2:1:1 or combined with fumaric acid yielded the highest propionate concentration across all treatments. We concluded that EOBs decreased methane production and nutrient degradability with better results with the individual EOB1 or EOB1/fumaric combination, which showed a potential enhancement in energy production.