Ruminal fermentation and in vitro digestibility of beef cattle fed monensin and monensin and virginiamycin or monensin and mineral traces + yeast combination in high-grains diets

This work was realized to study the antimicrobial activity, pH, ammonia, antioxidant activity, volatile acid fatty and in the liquor rumen of different additives combinations (monensin – MONE, monensin + virginiamycin – MO+VI and monensin + mineral traces + yeast – MO+MY) compared to control – CONT (without additives). The antimicrobial activity was studied against four strains of Gram-positives ruminal bacteria and seven strains of Gram-negatives ruminal bacteria. The concentration of MONE was 37.7 g/L, MO+VI was 42.7 g/L and MO+ML was 39.3 g/L. Cultivation was performed at 39° C, and bacteria growth was evaluated by quantifying the optical density (OD) at 600 nm using a spectrophotometer. Optical density was evaluated before and 8, 12, and 24 hours after incubation. The Ruminococcus albus, Ruminococcus flavefaciens and Lachnospira multipara bacteria growth was inhibited (P < 0.05) by MONE, MO+VI and MO+MY treatments at the three times (8, 12 and 24 hours). The greatest growth inhibition of these three bacteria occurred in the MO+VI treatment, in comparison with the MONE only or the MO+MY combinations. MONE e MO+MY treatments showed a sign of bacteriostatic activity; whereas the MO+VI treatment indicates a sign of bactericidal action. The three compounds studied showed inhibitory activity lower against Streptococcus bovis growth in the three studied periods (8, 12 and 24 hours). The greatest inhibitory activity was observed in the MO+VI additives’ combinations and the lowest for the MO+MY additives combinations, being intermediate for monensin only. The additives addition had a little effect on the microbial growth of Prevotella albensis and Prevotella bryantii bacteria, intermediary on Prevotella ruminicola and Anaerovibrio lipolyticus bacteria and strong activity on Ruminobacter amylophilus.