Feed efficiency and carcass traits of feedlot lambs supplemented either monensin or increasing doses of copaiba (Copaifera spp.) essential oil

Abstract The aim of this study was to evaluate dietary monensin (MON) and incrementing levels of copaiba ( Copaifera spp .) essential oil (CO) on nutrient intake, time spent eating and ruminating, performance, carcass traits, and meat quality of feedlot lambs. Sixty non-castrated Crossed White Dorper lambs were randomly assigned to the following treatments: control (CON), basal diet with no feed additives; MON, dietary inclusion of 25 mg/kg DM of MON (Rumensin ® , Elanco Eli Lilly and Company, Sao Paulo, Brazil); and copaiba essential oil (CO), dietary inclusion of 0.5, 1.0, and 1.5 g/kg DM of CO diluted into isopropyl alcohol (7 mL). Animals were fed a diet with 53:47 of forage to concentrate ratio. Monensin dietary inclusion was compared with the other treatments through Dunnett’s test, and the effects of CO levels were evaluated through linear and quadratic contrasts. Dry matter intake, average daily gain (ADG), and time spent eating were recorded through the feedlot period. Immediately after slaughtering and at 24 h postmortem, carcass traits were assessed and meat samples were taken to meat quality analyses, respectively. Control and MON-treated lambs had lower ADG in comparison with those fed CO at 0.5 g/kg DM. There was a positive quadratic effect on feed efficiency and ADG according to CO levels, wherein the highest values were observed in lambs fed CO at 0.5 g/kg. Nutrient intake was not affected by treatments. Copaiba essential oil provision linearly increased the time spent eating and quadratically affected the time spent ruminating while lambs were lying, wherein the highest value of time spent ruminating was found in lambs fed CO at 0.5 g/kg. Neither carcass traits nor subprimal yield were affected by CO levels, but MON-fed lambs had lower fat thickness and external length compared to CON and those CO-fed lambs. Copaiba essential oil provision at 1.5 g/kg increased cooking losses of Longissimus dorsi in comparison with MON. Further, CO supply at 1.5 g/kg increased Warner Bratzler shear force and decreased L* intensity in Semimembranosus meat in relation to MON. Copaiba essential oil had a negative quadratic effect on the ether extract content in Gluteo biceps . This study demonstrated that CO supplementation ranging from 0.5 to 0.75 g/kg can improve feed efficiency and ADG, consequently decreasing the feedlot time of lambs, and CO can be used in place of MON in feedlot lamb diets.