PS13-20. Effects of Immunomodulatory Additive Supplementation on Performance and Carcass Traits of Nellore Bulls in a Commercial Feedlot During the Heat Stress Season.

Abstract Heat stress represents a major challenge in tropical regions and can significantly impair animal performance in feedlot systems. Therefore, strategies aimed at mitigating heat stress during the finishing period are essential to optimize productivity. Nutritional additives designed to enhance the physiological status of animals may play an important role in alleviating the negative effects of heat stress. The objective of this study was to evaluate the effects of NutraGen® nutritional specialty product on the performance and carcass traits of Nellore bulls throughout a finishing period (114-day) in a commercial feedlot during the heat stress season in Brazil. A total of 5,250 Nellore bulls (30 months of age; initial body weight: 354.3 ± 27.9 kg) were randomly assigned to one of two groups: Control (n = 2,413) or NutraGen (n = 2,837; 7 g/100 kg of body weight). Animals in each group were randomly housed in 16 pens (164 head/pen), with free access to fresh feed and water. Animals were fed four times daily and received an adaptation diet for the first 21 days, followed by a finishing diet for 93 days. The additive was included in the diet for the NutraGen group. A heat stress day was defined as a day when the Heat Load Index (HLI; Gaughan et al., 2008) exceeded the threshold established based on animal and environmental inputs, as estimated using Combat® software (Phibro Animal Health). NutraGen was incorporated into the feed using the mixer truck and delivered daily as part of the diet. The additive was provided only on days when HLI exceeded the recommended threshold. Overall, HLI was estimated daily using a 10-day forecast. The average animal HLI was 94 and exceeded the environmental threshold during 76% of the feeding period (87 days). Performance parameters evaluated included, final body weight (FBW), average daily gain (ADG), carcass weight (CW), carcass daily gain (CDG), and dry matter intake (DMI). Performance data were analyzed using multivariate linear regression to estimate NutraGen effects, considering pen as the experimental unit and P-value with 5% of significance. Even with bulls having the same IBW at the beginning of the trial, those supplemented with NutraGen showed a greater FBW (+11.1 kg; P < 0.038) and tendency for CW (+4.3 kg; P < 0.078) compared with the control group. No significant differences (P ≤ 0.636) were observed for ADG (1.467 kg ± 0.06), CDP (55.50% ± 0.14), and DMI (9.78kg ± 0.31). In conclusion, supplementation with NutraGen during the heat stress season throughout the 114-day finishing period demonstrated improved performance and carcass traits in Nellore bulls. These results suggest that NutraGen® represents a promising nutritional strategy to mitigate the adverse effects of heat stress and help improve productivity in feedlot cattle. For image description, please refer to the figure legend and surrounding text.