Efecto del uso de aceites como aditivos nutricionales sobre la performance animal de novillos pastoreando sorgo forrajero durante el verano

The objective of this study was to evaluate the effect of using essential oils as a nutritional additive, together with supplementation with dried distiller’s grains (DDGS), on performance, ingestive behavior, and physiological indicators associated with heat stress in steers grazing forage sorghum during the summer. The experiment was conducted at the Mario A. Cassinoni Experimental Station, Paysandú, Uruguay, between January 16 and March 13, 2025 (56 days). Seventy-two Hereford steers with an average body weight (BW) of 285 ± 36.7 kg were blocked by BW and randomly assigned to three treatments (3 replicates per treatment; 8 animals per replicate): grazing without supplementation (Control); grazing with DDGS supplementation at 0.5% of BW; and grazing with DDGS supplementation at the same level plus a mixture of essential oils. Animals grazed forage sorghum under a rotational grazing system, with a forage allowance of 8 kg DM/100 kg BW during the first 28 days and 10 kg DM/100 kg BW during the final 28 days, and were housed during daytime with access to water and shade between 10:00 and 17:00 h. Results indicated that steers grazing forage sorghum without supplementation during summer achieved weight gains close to maintenance (0.070 kg/day). Supplementation with DDGS at 0.5% of BW significantly improved (P < 0.001) productive performance, increasing average daily gain (0.620 kg/day), an effect mainly attributed to the greater energy and protein supply from the supplement (supplementation response of 0.545 kg/day), with an average feed conversion efficiency of 2.73:1 and no differences among supplemented treatments (P > 0.05). Physiological and behavioral measurements suggest that, under the experimental conditions—where 87% of the experimental period was classified as being at risk of heat stress—essential oils did not contribute to improving thermal comfort in steers during the summer, as no clear positive response was observed in treatments including them. In this context, the use of an additive composed of cinnamaldehyde, silicic acid, mono- and diglycerides of fatty acids, and allicin (in proportions of 43, 37, 13, and 7%, respectively) did not show additional clear productive or physiological benefits under the evaluated conditions.