Ruminal Microbiology from Nellore Steers Supplemented with Additives in the Rainy Season

The aim of study was evaluate the ruminal microbiology from animals fed supplements with monensin (MN), virginiamycin (VM) or both associated (MNVM), in the rainy season.Twelve steers cannulated in the rumen (518.42 ± 55.40 kg) were housed in 12 paddocks (one animal on each paddock) of Brachiaria cv.'Xaraés' and supplemented daily with 0.3% of BW. The diets were: supplement without additives (SUPL), with MN (80 mg/kg), with VM (150 mg/kg) and associated supplement MNVM (80 + 150 mg/kg of MN and VM, respectively). The experiment consisted of four periods of 28 d (27 d of adaptation and 1 d of sampling collection). Animals were housed continuously in the paddocks with animals used in a trial for performance evaluating. The study evaluated the relative proportion of microorganism, R. albus, R. flavefaciens, F. succinogenes, S. ruminantium and methanogenic bacteria on 28^th and 118^th d of the experimental period (1^st and 4^th period). This design chosen to show the effect in the short and long term antibiotics. Data were analyzed as a completely randomly design with three replicates by treatment on each period, using the MIXED procedure of SAS. In the first period, the R. albus and methanogenics groups had no effect (P> 0.05) by the use of the two additives. Observed the effect (P <0.05) of VM and MNVM on the relative proportion of R. flavefaciens, F. succinogenes and S. ruminantium , however, the R. flavefaciens bacteria did not differ from the control group to MN. In the 4^th period the relative proportion of F. succinogenes, S. ruminantium increase when used VM and MNVM. The relative proportion of R. flavefaciens did not differ when compared to control group with used MN, however there was decrease the proportion with used VM and MNVM (P <0.05). The methanogenic group showed effect when used VM (P<0.05). In this study, the virginiamycin had greater control over R. flavefaciens, it is worth noting that the adaptive effect of bacteria was not conserved when the same additive was used.