Postparturient (type II) ketosis, mostly subclinical in degree, is a common disease associated with decreased milk production, decreased reproductive performance, and increased risk of displaced abomasum (DA) in dairy cattle. Based on the assumption that early treatment of ketosis will prevent the anticipated losses, it is often recommended to perform ketosis screen-and-treat programs in fresh cows. However, secondary prevention trials using cowside tests have yet to be published. Therefore, the extent of losses that may really be prevented by such intervention is unknown. The objective of this study was to evaluate the effect of treating ketosis cases found with a fresh cow screening program.