The effects of feeding a standardized mixture of essential oils vs monensin on growth performance, dietary energy and carcass characteristics of lambs fed a high-energy finishing diet

Thirty-six Pelibuey × Katahdin crossbred intact male lambs (28.5 ± 3.5 kg) were used in a 56-d experiment in a randomized complete block design to evaluate the effects of a standardized mixture of essential oils (EO) versus monensin sodium (MON) on growth performance, dietary energy, and carcass characteristics. Lambs were fed a corn-based finishing diet (13.8 % CP and 2.14 Mcal NEₘ/kg DM) supplemented with: 1) no additive (Control), 2) 30 mg MON/lamb, and 3) 150 mg EO/lamb. Water consumption of EO and Control lambs was not different. In contrast, lambs fed MON consumed 18.1 % less (P < 0.01) water than Controls and EO groups. Compared to Controls, EO improved (P < 0.05) gain efficiency, estimated dietary net energy (NE). Compared to MON, supplemental EO increased (P < 0.05) dry matter intake (DMI), average daily gain (ADG) and gain efficiency, and tended (P = 0.09) to increase estimated dietary NE. Compared to Controls, lambs fed MON decreased DMI and ADG but without showing difference on gain efficiency and estimated dietary NE. With the exception of carcass weight (lambs fed MON had lower hot carcass weight than Control and EO), there were no treatments effects on carcass composition. Compared with Controls, EO and MON supplementation decreased relative weights (as a proportion of empty body weight) of intestine and omental fat. Compared with MON, EO decreased relative weight of mesenteric fat. We conclude that compared with Control (non-supplemented) lambs, supplemental EO enhances feed efficiency, and dietary net energy. Compared with MON, supplemental EO enhances ADG. However, effects of MON and EO on feed efficiency and dietary net energy are not appreciable different. Supplemental EO did not negatively affect carcass characteristics or visceral organ mass. As such, supplemental EO is a viable alternative to the antibiotic monensin for enhancement of feed efficiency of finishing feedlot lambs.