Performance and Health Responses to Essential Oil Supplementation in Newly Received Beef Heifers Grazing Bermudagrass and Receiving a Limit-Fed Diet

Essential oils (EOs) have been investigated as natural feed additives due to their potential rumen-modulating and antioxidant properties. However, responses to EO supplementation have been inconsistent. The objective of this study was to evaluate the performance and health responses of newly received beef heifers grazing Bermudagrass (Cynodon dactylon) receiving a limit-fed diet with or without a commercial EO additive. A total of 72 crossbred beef heifers (235.4 ± 19.5 kg) were transported from Montgomery, AL, USA to the Southwest Research and Extension Center Stocker Unit (Hope, AR, USA). Cattle were processed, stratified by initial body weight (BW), and assigned to one of two treatment groups during a 42 d receiving period: (1) limit-fed diet only (2.0% BW; CON; n = 6 paddocks) or (2) the same limit-fed diet supplemented with an EO blend (FYT; 0.50 g/heifer/d; n = 6 paddocks). Cattle on both treatments had access to pastures composed of Bermudagrass. Body weight was recorded every 21 d until the end of the study. Average daily gain (ADG), BW, and gain:feed (G:F) were analyzed using SAS 9.4, with treatment as a fixed effect and block as a random effect. Pasture was the experimental unit. Health outcomes were analyzed using binomial distribution. No differences in BW were observed between treatments throughout the 42 d period (p > 0.05). When analyzed on a deads-in basis, FYT heifers had greater ADG and G:F (p ≤ 0.05) between D22 and D42. On a deads-out basis, FYT heifers had greater ADG and G:F from D0 to D21 (p ≤ 0.02) and across the 42 d period (p ≤ 0.04). Cumulative morbidity did not differ between treatments; however, a treatment × day interaction indicated that morbidity occurred earlier in FYT heifers. Overall, EO supplementation did not affect the final BW or cumulative morbidity, but it was associated with a greater gain efficiency during specific portions of the receiving period. These results suggest that the response to EO supplementation may vary with the period and method used to evaluate performance, and that additional research is needed.