Effect of lasalocid, monensin or thiopeptin on lactic acidosis in cattle.

Lasalocid, monensin or thiopeptin was administered intraruminally each at .33, .65 or 1.3 mg/kg body weight and evaluated for its effectiveness in preventing experimentally induced lactic acidosis in cattle. Four rumen-fistulated cattle were used for each dosage level and the design was a 4 x 4 Latin square with each animal receiving lasalocid, monensin, thiopeptin or no antibiotic. Acidosis was induced by intraruminal administration of glucose (12.5 g/kg body weight). Control cattle exhibited the typical drop in rumen pH and concurrent increases in L(+) and D(-) lactate concentrations commonly observed in cases of lactic acidosis. Alkali reserves were depleted in the control cattle as evidenced by a decrease in blood bicarbonate and a negative shift in base excess. In all three trials, cattle given lasalocid had higher rumen pH and lower lactate concentrations than did control cattle or cattle given monensin or thiopeptin. Cattle given monensin had a significantly higher rumen pH and a lower lactate concentration than the controls only at the .65 and 1.3 mg/kg body weight dosages, whereas thiopeptin was effective only at the 1.3-mg dosage. Concentrations of total VFA in rumen fluid decreased in the controls but remained unchanged in cattle given antibiotics. A significant reduction in the molar proportion of acetate and an increase in the molar proportion of propionate were observed in the rumen fluid of the cattle given antibiotics. Colony counts of Streptococcus bovis and Lactobacillus were significantly reduced in rumen fluid of cattle given 1.3 mg antibiotic/kg body weight. Counts of lactate-utilizing bacteria increased in both control cattle and cattle given antibiotics. Cattle given antibiotics showed no evidence of lacticacidemia, hemoconcentration or change in acid-base balance.