Influence of an oregano-based essential oil on growth performance and carcass traits of beef steers

The objective of this study was to determine the influence of an oregano-based essential oil on growth performance, health outcomes, and carcass characteristics of yearling beef steers finished in an all-natural program. Single-sourced yearling steers (N = 128; initial body weight [BW] = 335 ± 7.9 kg) were allotted to 16 pens (n = 8 pens/treatment with 8 steers/pen). Steers were blocked by pen location in a randomized complete block design (n = 8 blocks total). Treatment groups consisted of (1) control group fed no oregano-based essential oil product (CON) and (2) a group fed 4 g/steer daily of By-O-Reg + Beef (Advanced Ag Products, Canton, SD; OEO). Steers were individually weighed on d 0 (arrival), d 38, d 66, d 108, and d 149 for growth performance measures. Steers were transitioned from a 70% concentrate diet to a 90% concentrate diet over the first 14 d and remained on the finishing diet until d 149. The finishing diet provided 1.37 Mcal/kg of NEg. Steers were evaluated daily for indications of disease or visible digestive disorders by a trained technician blinded to the treatments. Steers were harvested at a commercial packing facility when they reached a common compositional endpoint determined by visual assessment. Prior to carcass chilling, hot carcass weight and liver score was recorded for each carcass. Following chilling, ribeye area, 12th rib backfat thickness, marbling score, USDA Quality grade, USDA Yield grade, and instrumental color (L*, a*, b*) were recorded. Health outcomes were not influenced by dietary treatment (P ≥ 0.18). Inclusion of OEO did not influence (P ≥ 0.73) carcass-adjusted final BW, dry matter intake, average daily gain, gain: feed, observed dietary net energy for maintenance (NEm) or net energy for gain (NEg), observed-to-expected dietary NEm or NEg. No differences (P ≥ 0.30) were observed between treatment groups for carcass traits or the distribution of USDA Yield and Quality Grades (P = 0.94 and P = 0.79 respectively). Collectively, growth performance, health, and carcass traits of steers finished in an all-natural program in this experiment were not influenced by dietary inclusion of an oregano-based essential oil feed additive.