USE OF VIRGINIAMYCIN AND SALINOMYCIN IN THE DIET OF BEEF CATTLE REARED UNDER GRAZING DURING THE RAINY SEASON: PERFORMANCE AND RUMINAL METABOLISM

The rumen is the most studied organ with regard to the symbiotic interaction between host and microbiota in the digestive tract of ruminants. Thus, this study aimed at evaluating the effects of including virginiamycin and salinomycin to the supplement for cattle fed tropical grass diet during the rainy season. Three treatments were set: control - mineral supplement COMIGO - Cria 61-F2 (MS); virginiamycin - MS + virginiamycin (Phigrow (r)) 100 mg/animal/day; salinomycin - MS + salinomycin (Posistac(r)) 108 mg/animal/day for the experiment 1 (performance) and experiment 2 (ruminal metabolism). The control showed higher Mineral supplement intake (MSI) (P 0.05) and better financial efficiency. Biometric measurements showed no differences (P> 0.05), suggesting a change in the ADG composition. There was no difference (P> 0.05) for dry matter digestibility (DMDIS), acid detergent fiber digestibility (ADFDIS), ruminal pH and ammoniacal-N. The virginiamycin had the highest effective neutral detergent fiber (NDF) degradability (P> 0.05) in the passage rates of 2 and 5%; the degradability rates were similar to control treatement and higher than that of salinomycin at the rate of 8%/hour. The virginiamycin or salinomycin can be conveyed to the MS, but do not promote significant effects on ruminal pH, ammoniacal-N, DMDIS and ADFDIS; but virginiamycin promoted greater effective degradability of NDF. Keywords: ammoniacal-N; antimicrobials; degradability; growth; ruminal pH