FEEDING MONENSIN OR ESSENTIAL OILS IN HIGH CORN OR BYPRODUCT FINISHING DIETS FOR NELLORE BULLS

Abstract Text: The objective of this study was to evaluate the effects of sodium monensin replacement for essential oils on behavior, DMI, ruminal pH and ammonium concentration in feedlot cattle. Sixteen Nellore bulls (339 ± 30 Kg initial BW) were allocated in individual pens to four 4 × 4 Latin square (LS) design, consisting of 21 d (including 14 d of adaptation). One of two basal diets used had 5% sugar cane bagasse, 50% wet corn gluten feed, 43.5% soybean hulls and 1.5% mineral and vitamin mix and the other had 80.6% ground corn, 12% sugar cane bagasse, 4% soybean meal, 0.9% urea, and 2.5% mineral and vitamin mix (DM basis). Each basal diet was used in two 4 × 4 LS. Feed additives were mixed within the mineral and vitamin mix according to treatments: 1) Control (CON), no additives;2) Monensin (MON), 25 mg/kg of DM (Rumensin^®); 3) Essential oil (EO), 0.5 g/kg of DM (commercial additive extracted from castor and cashew oils, Essential^®); and 4) Essential oil plus monensin (E+M), 0.3 g/kg of DM and 25 mg/kg of DM, respectively. There were no differences between the basal diets for DMI (8.2 kg/d), feeding and idle time (193 and 1104 min in 24 h), feeding frequency (9.5 feed/d) and meal size (22 min/feed). Supplementing essential oils at 0.5 g/kg of DM (EO) decreased (P < 0.05) rumination in 37% compared to control, 130 vs. 208, respectively. Essential oils only, or E+M increased (P < 0.01) ruminal pH and ammonia nitrogen, 6.06 and 6.01 vs. 5.79 and 5.89 mg/dL, respectively for EO, E+M, CON and MON. Feeding frequency was the only parameter affected (P < 0.05) when byproducts were used, with 12.9 and 8.1 meal/d, for CON and MON, EO and M+E, respectively. In conclusion, castor and cashew essential oils have some beneficial effects on cattle physiology in the short time, such as the 21 days adaptation period to high grain diets.

Keywords: feedlot, feed additives, ionophores