There are now a number of studies which confirm that lasix improves performance, on a very general basis said to be about 2 lengths. And for quite some time now it has been permitted as a theraputic medication in every major racing jurisdiction in the US. But the fact that it is permitted does not mean that it is entirely unregulated. The times when it can be administered and the maximum amount which can be administered still varies from state to state. And the "recommended" dosage is a broad range of anywhere from 250-500mg. These facts, together with the propensity some shrewd trainers & owners have for cashing bets at a price, make the 1st vs 2nd lasix angle one that bears some consideration. Hence, even though other factors might have been involved, and even though the sample sizes might be small, it is worth knowing, imho, that Duane Knipe has 10.5% winners 1st lasix, but has 42.5% winners 2nd lasix with an ROI of $4.78. Or that David Sam goes from 9.4% to 25%, or that Oran Trahan goes from 8.7% to 22.7%,etc.,etc. Of course, absent a particularized study, no one knows for certain how many of these horses ran a "better number" 2nd time lasix. But we do know the number of times they won, which if nothing else is some evidence that the trainers in question know where to spot their horses when the time is right. In terms of day to day racing, a pretty good argument can be made that in the final analysis that is the one skill that separates the good from the average trainer.