Breeding age ewes were studied to evaluate the effects of supplementing lasalocid sodium (Bovatec®) on ewe reproductive and lamb performance including the occurrence of peripartum metabolic disease. Periparturient serum chemistry profiles were monitored during transition. Lasalocid supplementation commenced before seven days before ram exposure for approximately 200 days until after weaning at a rate of 70mg head -1 day-1. However lasalocid was not found to have significant effects on performance outcomes, although positive and negative trends were noted. The ewe biochemical profiles reflected a healthy flock during transition and will provide useful reference values for future studies. There were no cases of periparturient metabolic disease observed during the study so no comparison to diseased biochemical profiles could be made. Analysis of the biochemical profiles identified BHB, NEFA, LDH and CK as useful predictors of a number of performance outcomes. Since no treatment effects were detected from supplementation with lasalocid there is no indication of a significant beneficial or detrimental consequence in healthy breeding ewes. The serum chemistry profiles presented in this study are useful reference values and appear to be useful in assessing the health status of periparturient ewes.