Thiopeptin for the prevention of ovine lactic acidosis induced by diet change.

Inclusion of thiopeptin, a sulfur-containing peptide antibiotic, at 0, 2.75, 5.5, 8.25, 11 and 22 ppm in the feed was evaluated in 8-week growth trials with 252 lambs. An abrupt diet shift to micronized milo at the start of the trials was used to provide a lactic acidosis challenge. Five of 78 control lambs died within 48 hr after the challenge. In lambs fed diets containing thiopeptin at levels of 11 ppm or more, there was no evidence of lactic acidosis. Lambs given thiopeptin at 11 ppm or more ate 11% more (P less than .05) and gained 20% more (P less than .05) than controls during the 8-week trial. Most of the improvement occurred during the first 2 weeks. Incidence of death was lower among lambs given thiopeptin at 2.75 to 8.25 ppm, but these animals showed no improvement in performance. In another study, abruptly shifting lambs to the micronized milo diet was found to provide an acute lactic acidosis challenge. After the shift, four of eight lambs developed ruminal lactic acidosis, with one dying of systemic lactic acidosis, with one dying of systemic lactic acidosis when plasma lactate exceeded 20 mumoles/ml. In affected lambs, ruminal lactate increased rapidly from an initial level of .2 mumoles/ml to over 130 mumoles/ml within 12 hr of consumption of the milo. Ruminal lactate returned to normal levels of less than 1 mumole/ml by 30 hr in lambs that recovered. High ruminal concentrations of lactate reduced total volatile fatty acids (VFA), and ruminal pH reflected total ruminal acids. Lactic acidosis did not occur in eight lambs after the switch to micronized milo when thiopeptin was included in the feed at 22 ppm. Ruminal lactate was reduced by 68% (P less than .01) and total ruminal VFA increased by 33% (P less than .05) in lambs fed thiopeptin in comparison with average levels in all controls.