PSXII-26 Withdrawing monensin by the end of finishing period increases intake and changes ruminal fermentation patterns of cannulated Nellore cattle

Abstract

This study, conducted at São Paulo State University feedlot, Dracena, Brazil, was designed to evaluate the effects of increasing diet energy content and withdrawing monensin (MON) by the end of the finishing period, while combined with virginiamycin (VM), on rumen fermentation patterns and DMI of Nellore cattle. The experiment was designed as a 5 x 5 Latin square, in which five 32-mo-old Nellore steers (531 ± 22 kg) cannulated in the rumen were utilized. Each period lasted 28-d, which was divided into phases as follows: 14-d adaptation (66% to 78% concentrate), 7-d finishing 1 (84% concentrate) and 7-d finishing 2 (88% concentrate). The treatments were: MON throughout phases, VM throughout phases, MON+VM throughout phases, MON+VM during adaptation and only VM during finishing 1 and 2, and MON+VM during adaptation and finishing 1 and only VM during finishing 2. Monensin and VM were added into diets at 30 and 25 ppm, respectively (DM basis). Rumen fermentation pattern was assessed by measuring ruminal pH and by collecting samples for SCFA determination on the last day of each phase. No treatment effect was observed (P > 0.05) for any of the SCFA variables measured, except for acetate:propionate, where cattle fed MON+VM throughout phases had greater ratio than those fed MON throughout phases on finishing 1 (P = 0.02; Table 1). Cattle consuming only VM in the study presented greater DMI throughout phases (P < 0.01), which did not negatively impact rumen pH (Table 2). Feeding MON+VM and withdrawing MON on finishing 2 did not affect SCFA concentrations, but decreased DMI, when compared to cattle fed VM either throughout phases or just during finishing, without affecting rumen pH. Thus, increasing diet energy content and withdrawing MON by the end of finishing period negatively impacted DMI without altering ruminal fermentation pattern.