375 Effect of natural additives as an alternative to monensin on the performance of Nellore males in a grazing system.

The study evaluated the potential of natural additives, essential oils (EO) and live yeast (LY), as alternatives to monensin (MON) to improve the performance of beef cattle in tropical grazing systems. 72 uncastrated Nellore males, 8 months old and 232 kg of initial body weight (BW), grazed on Urochloa grass, in a continuous grazing system in 12 paddocks (2 hectares each) for 416 days, 280 days for the growing and 136 days for the fattening phases. The animals had ad libitum access to feed and water. All animals were weighed after 16h fasting every 56 days. Animals were randomly distributed in four blocks designed with three treatments and 24 animals per treatment. Every 28 days, animals were moved to another paddock to eliminate possible paddock effects. The treatments during the growing phase were: protein supplement + MON, protein supplement + LY, and protein supplement + EO. The additives were added to the supplement and the average doses during the dry and rainy seasons, respectively were: MON (Rumensin) 172 and 150 mg/day, LY (ActiSaf SC47PWD) 4 and 2 g/day, EO (RumenPlus Pasture) 5 and 5 g/day. During the fattening phase, animals were semi-confined with high-concentrate (estimated daily intake of 1.8% of the body weight) with respective additives. The average doses were: MON (Rumensin) 279 mg/day, LY (50% ActiSaf SC47PWD and 50% Procreatin7) 5 g/day, EO (RumenPlus Feedlot) 5 g/day. Dry matter intake (DMI) was calculated using the indigestible neutral detergent fiber and Lipe® (external marker) to estimate total feces production. Carcass gain was calculated assuming a carcass dressing of 50% of initial BW and considering carcass gain post-slaughter. Average daily gain (ADG), carcass (weight and gain), BW, and DMI were analyzed using PROCMIXED in SAS, with treatment means compared via Tukey’s test. Significance was determined at P≤0.05, with trends noted at 0.05>P≤0.10. Results indicated that DMI was higher for LY compared to MON (P=0.0833), during the growing phase (dry season). In the fattening phase, MON had lower DMI compared to LY and EO (P=0.0022). However, there were no significant differences in Final BW, ADG, and carcass (weight and gain) among the treatments, during the growing and fattening phases. Essential oils or live yeasts are viable alternatives to Monensin for beef cattle performance in grazing systems.