Exogenous Enzyme Supplementation for Beef Cattle under Dry-Season Nutritional Strategies: Effects on Growth Performance, Nutrient Utilization and Ruminal Fermentation

This study evaluated whether the response of grazing beef cattle to exogenous fibrolytic enzymes depends on the nutritional supplementation strategy adopted during the tropical dry season. Two complementary experiments were conducted with Nellore steers grazing Urochloa brizantha cv. Xaraés. In Experiment 1, 102 steers were assigned to a completely randomized 2 × 3 factorial design with two supplementation strategies [protein supplement (PRO; 0.1% BW) or protein–energy supplement (PPE; 0.3% BW)] and three levels of a fibrolytic enzyme blend (0, 4.75, or 9.5 g/day). Experiment 2 used five rumen-cannulated steers in a 5 × 5 Latin square to evaluate nutrient intake and digestibility, ruminal fermentation, microbial protein synthesis, and nitrogen utilization. Protein–energy supplementation increased final body weight, average daily gain, nutrient digestibility, ruminal volatile fatty acid production, microbial protein synthesis, and nitrogen retention compared with PRO (P < 0.05). Enzyme supplementation produced dose-dependent responses, with quadratic effects on average daily gain and feeding behavior and greatest productive responses at intermediate inclusion levels. Under PPE, enzyme supplementation increased dry matter and neutral detergent fiber digestibility and enhanced acetate and propionate production, whereas microbial protein synthesis and nitrogen utilization were mainly influenced by supplementation strategy. Overall, the benefits of fibrolytic enzymes were associated primarily with improved digestive efficiency and ruminal fermentation rather than increased feed intake. These findings indicate that the efficacy of exogenous fibrolytic enzymes under tropical dry-season grazing depends on the nutritional environment and is enhanced when enzymes are incorporated into protein–energy supplementation strategies.