Effects of capsaicin and monensin on ruminal fermentation, intake, nutrient digestibility, and ruminal dynamics of grazing bulls

Dietary supplementation with feed additives may influence intake, nutrient digestibility, and ruminal fermentation in grazing cattle. The objective of this study was to evaluate the effects of supplementation with capsaicin and/or monensin on intake, nutrient digestibility, energy balance, blood parameters, ruminal kinetics, ingestive behavior, and ruminal fermentation of grazing bulls. Four crossbred (Holstein × Zebu) bulls (375 ± 14 kg body weight (BW); 24 ± 1 months of age), fitted with rumen cannulas, were assigned to a 4 × 4 Latin square design and maintained on 1.2 ha of Pangola grass (Digitaria decumbens) pasture with supplementation at 0.3 % of BW. The bulls were allocated to the following treatments: (1) control (CON): supplementation without additives; (2) capsaicin (CAP): supplementation including 100 mg kg⁻¹ of total dry matter (DM) of capsaicin (CAPCIN®, NutriQuest, São Paulo, Brazil); (3) monensin (MON): supplementation including 20 mg kg⁻¹ of total DM of sodium monensin (Poulcox 40®, Huvepharma, Bulgaria); and (4) capsaicin + monensin (CAPMON): supplementation including sodium monensin (20 mg kg⁻¹ DM) and capsaicin (100 mg kg⁻¹ DM). Supplementation with CAP and MON increased the total tract digestibility of organic matter (OM), crude protein (CP), and neutral detergent fiber (NDF) compared with CAPMON supplementation. A tendency toward a greater ruminal DM pool was observed in bulls supplemented with CAPMON compared with those receiving CAP and MON, whereas bulls supplemented with MON showed higher passage and turnover rates of potentially digestible neutral detergent fiber (_tdNDF) than those supplemented with CAP. Bulls receiving CAPMON spent more time grazing (min d⁻¹) compared with those supplemented with CAP and MON. In addition, bulls supplemented with CAP and MON exhibited higher ruminal pH and lower propionate concentration than those supplemented with CAPMON. The use of capsaicin and/or monensin at the evaluated doses may be applied in animal production.