Feed additives based on essential oils (EOs) have emerged as a potential alternative to ionophores for diets with elevated grain inclusion. Also, on some occasions, EOs have been used in combination with monensin, with variable results. A metabolism trial was conducted using a 2 × 2 factorial arrangement of treatments, evaluating supplementation with (A) monensin sodium (0 mg/steer daily vs. 400 mg. steer daily) and (B) a blend of EOs (eugenol, linalool, anethole, and cinnamaldehyde, 0 g/d vs. 14 g/d). Four Red Angus steers (BW = 435 ± 9.0 kg) with ruminal and duodenal cannulas were used, and the study was conducted as a Latin square with four periods of 28 days each. Ruminal fermentation and nutrient digestibility at different levels (ruminal, intestinal, and total tract) were determined. The EOs increased total tract starch digestibility (p = 0.05) by 4.5% and propionate concentration (p = 0.03) by 30.9%. Furthermore, EOs decreased acetate (p = 0.04) by 7.4% as well as the acetate to propionate ratio (p = 0.03). In conclusion, our results suggest that it is safe to combine this EO blend with monensin for feedlot diets. The EO blend improved starch digestibility and increased efficiency of the ruminal fermentation end-products, which suggests it could be beneficial in diets based upon grain.
Podversich et al. (Wed,) studied this question.