Diet supplementation with a mixture of essential oils: Effects on enteric methane emissions, apparent total-tract...

This study examined the effects of supplementing dairy cows with a mixture of essential oils on enteric CH₄ emissions, apparent total-tract nutrient digestibility, N utilization, and lactational performance (production, components, and efficiency). Thirty-two multiparous lactating Holstein cows were used in a randomized complete block design. Cows averaged (mean ± SD) 95 ± 15.4 DIM, 47.7 ± 4.51 kg milk yield, and 698 ± 68.2 kg BW at the start of the experiment. The experiment consisted of a 3-wk pretreatment period (i.e., covariate), followed by a 3-wk adaptation to the experimental treatments, and a 10-wk period for data and sample collection. At the beginning of the study, milk yield and DIM data were used to block the cows into 16 blocks of 2 cows each. Subsequently, the blocks were adjusted based on milk yield and enteric CH₄ emission data collected during the pretreatment period. Within each block, cows were assigned to 1 of 2 dietary treatments: (1) a basal diet supplemented with a placebo (control, no additive), or (2) a basal diet with the essential oil supplement (Agolin, 1 g/cow per day). The basal diet (i.e., TMR) was composed of 69.3% forage (corn and alfalfa silage and grass hay) and 30.7% concentrate, on a DM basis, and the essential oil mixture consisted mainly of coriander seed oil, eugenol, geraniol, and geranyl acetate. Twice daily, the essential oil supplement was thoroughly mixed with 50 g of a commercial protein supplement (i.e., carrier) and 500 g of the TMR and this premix (i.e., 550 g/meal) was offered to the cow before the basal diet. No interactions between the essential oil supplement and the sampling week were observed for any of the response variables. Dry matter intake, apparent total-tract nutrient digestibility and N balance were unaffected by feeding the essential oil supplement. Yields of milk, 4% FCM, and ECM were not modified by the experimental treatment. Neither feed efficiency (kg milk/kg DMI, kg 4% FCM/kg DMI, kg ECM/kg DMI) nor dietary N use efficiency in milk N secretion (i.e., g milk N/g N intake) were affected by essential oil supplementation. Body weight change and BCS did not differ between cows fed the essential oil supplement versus cows fed the control. Daily enteric CH₄ production, CH₄ yield, and CH₄ intensity averaged 498 g/d, 18.4 g/kg of DMI, and 11.0 g/kg of ECM, respectively, and were unchanged by essential oil supplementation. We conclude that supplementing cows fed a high-forage diet with 1 g/d of this essential oil mixture did not positively affect lactational performance, nutrient digestibility, and N utilization, or reduce enteric CH₄ (production, yield, and intensity). More research is needed to identify the optimal dose of this essential oil mixture and elucidate how it may interact with the basal diet to improve the mixture's efficacy.