Ninety crossbreed bulls (349.5 ± 8.25 kg initial weight) were used in an 87day trial to compare the effects of a blend of essential oils plus 25-hydroxy-Vit-D3 (EO + HyD) versus the combination of monensin with virginiamycin (MON + VM) on feedlot growth performance and carcass characteristics. Dietary treatments (nine replicates/treatment) were supplemented with 40 mg/kg diet dry matter of MON + VM (equal parts) or with 120.12 mg/kg diet dry matter of a combination of standardized mixture of essential oils (120 mg) plus 0.12 mg of 25-hydroxy-vitamin-D3 (EO + HyD). There were no treatment effects on dry matter intake (DMI, p = 0.63). However, the coefficient of variation in day-to-day DMI was greater for EO + HyD than for MON + VM (11.4% vs. 3.88%, p = 0.04). There were no treatment effects (p ≥ 0.17) on daily weight gain, gain-to-feed ratio, and estimated dietary net energy. Cattle supplemented with EO + HyD had greater Longissimus muscle area (7.9%, p < 0.01) and estimated retail yield (1.6%, p = 0.03), and tended to have heavier (1.7%, p = 0.10) carcass weight. Differences among treatments in dressing percentage, fat thickness, kidney–pelvic–heart fat, and marbling score were not appreciable (p > 0.10). It is concluded that growth performance response and dietary energetic are similar for finishing cattle supplemented with EO + HyD vs. MON + VM. However, compared with MON + VM, supplementation with EO + HyD during the finishing phase may improve carcass Longissimus area and carcass yield.

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 less than 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.

Forty-eight Pelibuey × Katahdin male intact lambs (25.12 ± 3.79 kg LW) were used in a 70-d growing-finishing trial. Dietary treatments consisted of total mixed corn-based diet supplemented with: (1) no feed additives (Control); (2) 150 mg of essential oils blend plus 0.10 mg of 25-hydroxy-Vit-D3/kg diet offered throughout the 70-d experimental period (EOD3); (3) Control diet fed during the first 35 days and zilpaterol hydrochloride (ZH) supplementation at 6 mg/kg diet offered during the final 35 days of the experiment (32 days with ZH with a withdrawal 3-d before harvest), and (4) basal diet supplemented with EOD3 during first 35 days finishing, and EOD3 in combination with ZH (EOD3 + ZH) during the subsequent 32-days with ZH withdrawal 3 days before harvest. The temperature–humidity index during the experiment averaged 80.4 ± 3.2. There were no treatment interactions (p > 0.20) on growth performance and carcass measures. Supplemental EOD3 did not affect (p = 0.43) dry matter intake (DMI), but increased (p < 0.01) carcass adjusted average daily gain (ADG, 9.2%), gain efficiency (GF, 6.7%), and observed vs. expected dietary net energy for maintenance (NE_m, 4.8%) and for gain (NE_g, 6.4%). Supplemental ZH did not affect dry matter intake (DMI, p = 0.50) but increased (p < 0.01) carcass adjusted ADG (14.5%), GF (13%) and observed vs. expected dietary NE_m (9%) and NE_g (11.7%). Compared to control lambs, the combination of both additives increased ADG (24.9%), GF (21.2%), and observed vs. expected dietary NE_m and NE_g (14.2% and 18.9%, respectively). There were no treatment interactions on carcass characteristics, visceral organ mass, or on gene expression of IGF1, IGF2 and mTOR in longissimus muscle (LM). Supplemental EOD3 increased hot carcass weight (HCW; 4.0%, p < 0.01) but did not affect other carcass measures. Supplemental EOD3 decreased (3%, p = 0.03) intestine mass weight (g intestine/kg empty body weight). Supplemental ZH increased HCW (6%, p < 0.01), dressing percentage (1.7%, p = 0.04), and LM area (9.7%, p < 0.01), and decreased kidney-pelvic-fat percentage (16.2%, p < 0.01), fat thickness (14.7%, p = 0.03), and visceral fat. Compared to controls, the combination of EOD3 with ZH increased HCW (10.2%). It is concluded that growth performance responses to supplemental EOD3 and ZH are additive. Both supplements can be fed in combination without detrimental effects on expected benefits when fed separately. In addition, ZH supplementation improves carcass traits.

Due to their specific properties, the autolyzed yeast Saccharomyces cerevisiae (SC) and bacterial Bacillus subtilis (BS) theoretically can have a synergistic effect when combined and offered in ruminant diets. Thus, the aim of this experiment was to evaluate the effect of their combination as feed additives on growth performance, dietary energy, carcass traits, and visceral organ mass in finishing lambs. For this reason, 48 Pelibuey × Katahdin lambs (98 ± 17 d age; initial weight = 20.25 ± 3.37 kg) were used in a feeding trial lasting 83 d. Lambs were blocked by weight and assigned to 24 pens. Treatment consisted in supplementing a high-energy diet with probiotic and/or prebiotic as follows: (1) finishing diet without probiotic or prebiotic supplementation (Control), (2) finishing diet supplemented with 1.5 g SC/kg diet, (3) finishing diet supplemented with 1.5 g BS/kg diet, and (4) finishing diet supplemented with 1.5 g SC plus 1.5 g BS/kg diet. There were no synergistic (interaction) effects by combining SC + BS in any of the variables evaluated. Lambs that were supplemented with BS showed a very similar response on dry matter intake (DMI, p = 0.41), average daily gain (ADG, p = 0.64), carcass traits (p ≥ 0.08), tissue composition (p ≥ 0.32), and relative visceral organ mass (g/kg EBW, p ≥ 0.15) than non-supplemented lambs. Compared to the control group, lambs that received SC alone or in combination with BS showed greater average daily gain (12.0%, p = 0.03), gain efficiency (6.1%, p = 0.04) and observed-to expected dietary energy efficiency (5.5%, p = 0.04). Supplemental SC and SC + BS increased hot carcass weight (p = 0.04) without effects on the rest of the variables evaluated including the shoulder tissue composition whole cuts, and visceral organ mass. It was concluded that SC improves growth performance and dietary energy in finishing lambs without changes in carcass traits or carcass composition. Combining SC with BS did not improve the magnitude of the response of SC supplemented alone. In this study, the inclusion of a 1.5 g/kg diet of BS during a long-term period (83 d) did not show benefits to finishing lambs.

Context: The beta-agonist zilpaterol (ZH) is a feed additive that improves growth performance via protein accretion during the finishing phase of ruminant fattening. However, evaluating the possible interaction between ZH and nutrients of the diet has received limited attention. Aims: We investigated the changes in growth performance and carcass traits in response to ZH supplementation of hairy lambs fed finishing diets with different energy concentration. Methods: Forty-eight Pelibuey × Katahdin crossbred male lambs (43.8 ± 6.3 kg) were used in a 34-day feeding trial to evaluate the interaction between diet energy density [8.37 (LE) and 8.79 (HE) MJ of net energy for maintenance (NEm) per kilogram of diet] and zilpaterol hydrochloride supplementation (ZH, dosed at 0 or 6 mg ZH/kg) on growth performance, carcass traits, and visceral mass. All diets contained 14.5% crude protein (CP). Key results: There was no interaction of energy level and ZH in any of the variables evaluated. HE increased average daily gain (ADG) and gain efficiency (GF) without affecting the observed-to-expected dietary NE. Zilpaterol supplementation increased ADG, GF, and observed-to-expected dietary NE. Both HE and ZH increased carcass weight. HE increased carcass fat, whereas ZH decreased it. HE increased dressing percentage. ZH increased longissimus muscle area, the muscle:fat ratio in the shoulder, and leg whole-cut proportion. Visceral mass was not affected by energy level. ZH decreased visceral fat. Conclusions: Increasing diet energy from 8.37 to 8.79 MJ NEm/kg enhanced growth performance and carcass traits but did not improve dietary energy utilization. Supplemental ZH enhanced growth performance, dietary-energy utilization and carcass traits of lambs. Implications: ZH supplementation is a tool to enhance growth performance by improving protein accretion and reducing carcass fat. Response to ZH supplementation is independent of the differences in energy density of finishing diets.