With the growing use of crossbred cattle in Brazilian feedlots and increasing pressure to reduce antibiotic use as growth promoters, this study examines the impact of three feed additives—monensin (MON), monensin with Lithothamnium calcareum (LCM), and a blend of essential oils (BEO)—on the performance of Nellore (NEL) and crossbred (CROSS) cattle. A total of 90 Nellore and 90 crossbred bulls were assigned to a completely randomized block design with a 2 × 3 factorial design for 112 days, and all received the same diet with varying additives. Their methane (CH₄) emissions were estimated. All data were analyzed using the emmeans package of R software (version 4.4.1). Crossbred cattle outperformed Nellore in average daily gain (ADG), hot carcass weight (HCW), and dry matter intake (DMI), though feed efficiency remained unaffected. Across additives, no significant differences were observed in ADG, HCW, or dressing percentage. However, LCM had a lower DMI than the BEO, while MON showed better feed efficiency than the BEO. A breed-by-additive interaction trend was noted for DMI as a percentage of body weight (DMI%BW), with Nellore bulls on LCM diets showing the lowest DMI%BW. Crossbreeds had greater net energy (NE) requirements for maintenance (NEm) and gain (NEg), and MON-fed animals had greater NEm and NEg than the BEO. Crossbred bulls had greater daily methane (CH₄) emissions than Nellore bulls. Animals on the BEO had greater daily CH₄ emissions and greater g CH₄/kg metabolic BW than LCM bulls. In conclusion, the addition of Lithothamnium calcareum to monensin did not enhance performance compared to monensin alone. Monensin outperformed the BEO in feed efficiency and nutrient utilization.

Three experiments were conducted to evaluate the effects of narasin inclusion on the growth performance of grazing beef cattle under similar forage availability and quality. All three experiments were arranged in a randomized complete block design according to the initial BW. Exp 1: 200 Nellore calves (initial BW = 177 ± 15 kg) were randomly allocated in three treatments for 84 d during the rainy season: (1) CONT: mineral supplement; (2) 1400 N: 1400 mg of narasin/kg of supplement; and (3) 2100 N: 2100 mg of narasin/kg of supplement. Narasin inclusion increased (p ≤ 0.01) ADG by 0.077 kg/d and final BW by 6.7 kg, with no differences (p ≥ 0.50) between narasin doses. Exp 2: 240 Nellore calves (initial BW = 195 ± 19 kg) were allocated to CONT or N1400 for 112 d during the rainy season. Narasin inclusion increased (p ≤ 0.01) ADG by 0.082 kg/d and final BW by 9.1 kg. Exp 3: 150 Nellore yearlings (initial BW = 332 ± 22 kg) were allocated for 112 d during the dry season: (1) PROT: protein supplement and (2) PROT250: inclusion of 250 mg of narasin/kg of supplement. Narasin inclusion increased (p ≤ 0.04) ADG by 0.048 kg and final BW by 5.3 kg. For all experiments, narasin inclusion did not impact (p ≥ 0.25) supplement intake. Hence, inclusion of narasin in mineral and protein supplements consistently enhances growth performance of grazing beef cattle across different seasons and production stages, without impacting supplement intake, providing an effective nutritional strategy to enhance productivity on tropical pastures.

Three experiments were conducted to evaluate the effects of narasin inclusion on the growth performance of grazing beef cattle under the same availability and quality forage conditions. All three experiments were arranged in a randomized complete block design according to the initial BW of each experiment. Exp 1: Two hundred Nellore calves were allocated in three treatments: 1) CONT: mineral supplement; 2) 1400N: inclusion of 1400 mg of narasin/kg of supplement; and 3) 2100N: inclusion of 2100 mg of narasin/kg of supplement. Narasin inclusion increased (P ≤ 0.01) ADG and final BW, with no effect (P ≥ 0.50) between doses of narasin supplementation. Exp 2: Two hundred and forty Nellore calves were allocated into two treatments: CONT and N1400. The inclusion of narasin increased (P ≤ 0.01) cattle ADG and final BW. Exp 3: One hundred and fifty Nellore yearlings were allocated in two treatments: 1) PROT: protein supplement, and 2) PROT250: inclusion of 250 mg of narasin/kg of supplement. The inclusion of narasin in the protein supplement increased (P ≤ 0.04) cattle ADG and final BW. In conclusion, the inclusion of narasin in mineral and protein supplements increased the growth performance of cattle on tropical pastures without changing supplement intake.