PSXIV-25 Monensin and immunomodulator additive in intensive pasture finishing of Nellore bulls.

Abstract Combined supplementation with additives is a tool to increase animal performance in grazing systems. Monensin is a commonly used ionophore and understanding the combined effects and its replacement with other additive mixtures is essential for developing nutritional strategies. The study aimed to evaluate the performance, carcass traits, and meat quality of young Nelore bulls fed supplements containing monensin (MON) or an immunomodulatory additive (IMN), composed of a mixture of natural bentonite, butylated hydroxytoluene, organic chromium, turmeric, chelated copper amino acid, lysine, microencapsulated essential oils, yeast cell wall, selenium proteinate, Saccharomyces cerevisiae, vitamin E, and chelated zinc, during the intensive pasture finishing phase. Eighty young Nelore bulls, with an initial body weight of 403.05 ± 41.27 kg, were distributed into 0.25-hectare paddocks with Brachiaria brizantha pasture, with 5 animals per paddock. A randomized block design was used, with initial fasted body weight as a local control measure, in a 2 x 2 factorial arrangement (IMN, with and without; MON, with and without). The treatments were: (1) supplement = without additives (CTR); (2) supplement with immunomodulatory additive (IMN 2.2 g/animal/day); (3) supplement with monensin (MON 200 mg/animal/day); or (4) supplement with monensin and immunomodulatory additive (MON+IMN 200 mg MON + 2.2 g IMN/animal/day). The experimental period lasted 102 days. The supplements with a composition of 880.4 g of dry matter; 155.4 g of crude protein; and 254.4 g of neutral detergent fiber, were provided at 2.0% of body weight. Blood plasma was collected 24 hours before slaughter. The fixed factors MON (with and without) and IMN (with and without) resulted in four treatments with four replications. The experimental unit was the paddock. Statistical analysis was performed using SAS® OnDemand for Academics, through the MIXED procedure, considering paddock as a random effect. Significance was considered when P < 0.01. After slaughter, subcutaneous fat thickness, meat color, cooking loss, and shear force were evaluated (P > 0.05). Bulls that received IMN showed increased supplement intake (P < 0.02) and final body weight 29.6 kg higher than CTR, with MON (27.0 kg) and IMN+MON (29.6 kg), and increased average carcass gain. Supplementation, when combined with MON+IMN, increased hot carcass weight (P < 0.03) and decreased plasma alkaline phosphatase (P < 0.03). Therefore, immunomodulatory additives emerge as a viable tool to improve animal performance in combination with or as a replacement for monensin.