Background: During the first stage of fattening, performance of cattle is more affected by high ambient load. A strategy to mitigate the negative effects of high ambient temperatures on energy efficiency is by monensin supplementation. However, the present concern about the use of antibiotics as feed additives has led to search for safe alternatives. Due to its nature, essential oils and supplementary vitamin D3 represent a potential substitute to monensin in cattle subjected to high environmental heat load. For this reason, The objective of this study was to compare supplemental monensin vs the novel combination essential oils plus vitamin D3 on growth performance and dietary NE of feedlot bulls exposed to elevated ambient temperature during the initial 84-d on feed.
Methods: Ninety crossbreed young bulls (228.0±7.1 kg initial weight) were used in 84-d trial to evaluate a blend of essential oils plus 25-hydroxy-Vit-D3 as a feed additive to alleviate the harmful effects of the high-ambient temperature on feedlot cattle performance during the early-growing phase. Dietary treatments (9 replicates/treatment) were supplemented with: 1) 24 mg of sodium monensin/kg diet DM (MON), or with 2) 119.12 mg/kg diet DM of a combination of standardized mixture of essential oils (119 mg) plus 0.12 mg of 25-hydroxy-vitamin-D3 (EO+HyD). Average THI was 82.7±3.2.
Result: There were no treatment effects on day-to-day fluctuations in DMI. However, EO+HyD tended to increase DMI (4.3%, P=0.06). Supplemental EO+HyD increased daily weight gain (8.3%, P<0.01) and gain-to-fed ratio (4.0%, P=0.03). Supplemental EO+HyD tended to increase estimated dietary net energy (2.5%, P=0.07) and observed-to-expected dietary NE ratio (3.0%, P=0.07). This effect can be attributed to a 7% reduction in the maintenance requirement. The combination of EO+HyD may be a valuable tool to optimize growth-performance and feed efficiency of cattle under conditions of high ambient heat load.
