The Lasix debate: the Scientists muddy the waters
The debate over the use of race-day medication, in particular the use of Lasix in North America has been heating up over the past year or so being fueled by the Jockey Club and WHOA on one side and the Horsemens/Trainer/Veterinary groups on the other. Lines have been drawn on the argument and battle cries/talking points well rehearsed with most of it rather emotive and little being based on the science of EIPH at all.
The scientific community has published pretty extensively on the use of Lasix/Furosemide for a number of years. There are over 20 papers on its use but here is a brief run down (papers are linked) on the papers that mattered most.
The famed South African study on 167 horses found that the pre-race use of Lasix reduced the severity of EIPH in racehorses. This is the study that is cited most by the pro-lasix crowd and was very well constructed and ironically partially funded by the Jockey Club.
The use of lasix has an effect on reducing the accumulated oxygen deficit. That is, it takes longer to run to fatigue with lasix use.
The use of lasix is performance enhancing in that improvement of performance in the furosemide trials was due more to the weight-loss related effects of the drug than its apparent alleviation of EIPH (this was a small study that needed more horses).
The one time alternate to Lasix, aminocaproic acid, is useless in reducing EIPH.
Lasix has a buffering effect on lactate production in racehorses which is why the TCO2 levels are higher in North America than anywhere else.
EIPH is highly heritable. There was a South African study done on 65,000 horses but the more recent Australian Study completed on 117,000 horses had the same findings.
There is a linear effect of Lasix administration to TC02 levels. That is, the more lasix you give, the more 'buffering' effect you get (the reason why a set Lasix dose is important).
The use of Lasix has an effect on calcium balance in horses up to 72 hours post administration. The long term effect of continued Lasix use isnt known on calcium levels.
Two larger EIPH studies were undertaken last year and earlier this year and their results are just now being published after peer review.
Last month Dr Preston and colleagues had their paper published in the Equine Veterinary Journal and concluded that while EIPH is common and varies in severity between individuals that there is no difference in racing career longevity between EIPH positive and EIPH negative horses trained and raced without the use of Lasix. The study was based on 822 imported horses into the tightly controlled Hong Kong racing environment and was hailed by the 'anti-lasix' crowd as a reason to take horses off raceday lasix - they can have normal length careers without it. After making its way into the mainstream in the Thoroughbred Daily News, the paper was so popular that the editor of the Equine Veterinary Journal decided to make it an open access article for all to download.
Arriving as accepted articles for the Equine Veterinary Journal this week is a paper by the same group that did the original South African study on 167 horses. This time they examined 1,000 horses racing in South Africa and found that EIPH was associated with impaired performance in Thoroughbred racehorses not medicated with furosemide and not using nasal dilator strips. Additionally, they performed a meta-analysis of the 17 studies that have been completed on EIPH and Lasix use and found that there is high quality evidence, albeit limited, that administration of furosemide reduces the incidence and severity of EIPH in Thoroughbred or Standardbred racehorses.
So there you have it. Two papers that seem to have opposite findings, but there is a nuance here. The Preston/Hong Kong paper found that EIPH didn't reduce career length. Horses had normally long careers with EIPH. This new South African study didnt refute that finding but showed that horses that were EIPH negative were >2 times more likely to win races, finished an average of one length ahead of horses with EIPH, and were 2.5 times more likely to be in the highest decile in race earnings when compared to horses with EIPH. So the takeaway is that horses can have a perfectly normal career length even if they have EIPH but that if they do have EIPH they aren't going to be as good as those that don't have it.
It will be interesting to see if this new paper gets as much mainstream airtime as the Preston/Hong Kong paper did.