Comparison of different additives on the prevention of ruminal subacute acidosis in beef cattle

Abstract

This project aims to comparatively evaluate the effectiveness of the antibiotic virginiamycin and the ionophore monensin in the prevention of subacute rumen acidosis (SARA) in cattle. We will use 24 female, 36 month-old steers, fitted with rumen cannula and weighting 300 kg. The animals will be kept in individual pens and fed with basal diet calculated at 2.5% of body weight of 75% D.M. of coast-cross hay and 25% concentrate with 80 % corn bran and 20% soybean meal and before the beginning of the experiment will undergo 30 days of adaptation period and recovery for surgery. The 24 animals are randomly distributed according to the weight in four groups of six animals each, as follows: control (C), virginiamycin (V), monensin (M) and monensin + virginiamycin (VM). The control group will receive only the basal diet while the V group will receive virginiamycin; M group will receive monensin and MV group will receive both additives. The doses of monensin and virginiamycin will be 187.5 and 300 mg/animal/day, respectively, administered directly throughout the rumen cannula when the offering of food. After 30 days of supplementation of the additives it will be performed experimental induction of ruminal acidosis in all animals by administration of citrus pulp directly into the rumen, according to the classical protocol. The animals will be clinically assessed at the following times: zero (baseline) and after three, six, nine, 12, 15, 18 and 24 hours of induction of SARA. Physical examination will be performed with emphasis on the number of heartbeats, respiratory rate, rumen movements and rectal temperature, in addition to recording the main clinical symptoms suggestive of SARA. At the same moments of clinical evaluation samples of rumen content, urine and blood will be collected. On rumen content the following variables will be evaluated: ruminal pH, redox potential, methylene blue reduction time, L-lactate, short chain fatty acids, osmolarity and titratable acidity. In the urine, the pH and specific gravity will be evaluated. On blood samples we will determined: packed cell volume, L-lactate concentration, plasma volume deficit, osmolarity and blood gas analysis. At the end of the experiment all cattle that present clinical picture of lactic acidosis be treated promptly and followed until their full recovery. Two-way repeated measures analysis of variance for will be carried considering the factors group and time, followed by Bonferroni test. A significance level of 5% is assumed. (AU)