Few racehorses compete without furosemide, a diuretic known commercially as Lasix, to reduce bleeding in the lungs, or exercise-induced pulmonary hemorrhage (EIPH). Horsemen and armchair veterinarians alike have questioned whether horses suffer a long-term impact from repeated dosing of furosemide. Furosemide causes horses to lose sodium, and they might not be able to make up that deficit by just licking a salt block. Sodium is essential for proper nerve function, so a sodium deficiency might decrease performance.
Renowned emeritus professor Dr. Katherine Houpt and her colleague Dr. Pamela Perry at Cornell University studied how furosemide affects the normal water and salt balance of horses who receive the drug chronically.
Houpt and her team used a herd of ponies at Cornell for the study, as the specially-outfitted urine collection stalls available for the research were too small to accommodate a Thoroughbred. The ponies were administered furosemide daily for three weeks. Researchers measured the ponies' water and sodium losses caused by the furosemide and the ponies' water and salt intake as they strived to replace those losses. The team took the same measurements for three weeks prior to furosemide administration to establish a baseline.
Houpt's team found furosemide caused an acute increase in salt and water intake, and the salt consumption persisted for the three weeks of the study, reaching a peak at day 10.
“Despite the increase in sodium chloride intake, four of the six ponies took in less sodium than they excreted in the urine,” Houpt reported. “This indicates that horses do not accommodate behaviorally to the physiological effects of the drug for at least three weeks.”
In other words, the ponies were unable to adjust their sodium balance to normal by just licking a salt block.
The ponies in the study led a sedentary life, and the study was performed in cool weather, so they didn't lose water and sodium via sweat. But Houpt is concerned that racehorses, which sweat during exercise, might be drawing sodium from their bodies if they cannot make up the deficit by licking a salt block.
“Sodium has to go into the cells for the nerves to fire,” Houpt said. “So if you've got low enough sodium, you would have problems. … you probably would see poor performance in these horses if they didn't make up for their salt loss.”
The study also showed that furosemide causes salt craving, so in some horses its administration might defeat its intended use, which is to reduce blood pressure so blood vessels in the lungs don't burst during exercise.
“If the horse has a greater blood volume because he's eaten more salt, then he may have higher blood pressure and that means he's more likely to bleed, so it could become a vicious circle,” Houpt said.
The obvious solution is to stop administering furosemide to racehorses, Houpt said. In the meantime, she suggested horses be offered salt to encourage them to correct the imbalance as much as possible, but the method of salt delivery could make a big difference.
“Make sure that they always have a block of salt,” Houpt said. “The advantage of the block of salt is that the horse will self-regulate, whereas if you mix it in his feed, he needs the calories, so he's going to [consume the salt] whether he needs it or not. So, it's better to have it available to him, and certainly available to him as soon as he comes off the racetrack, so that he can make up for the deficit he acquired when they gave him Lasix.”
Houpt acknowledged her study has been criticized, mainly because it was done with ponies instead of exercising Thoroughbreds, and because the animals received furosemide daily. She agreed that further study should be conducted with Thoroughbred racehorses under typical management and receiving furosemide only when they work out or race.
“Care must be taken in performing horses that they have access to salt and water,” the report concluded. “The horse will consume more salt, but will not be able to meet their acute needs while performing. Conversely, salt access should probably be restricted when the goals is to lower blood pressure or reduce edema. The long-term consequences to the horse's performance and health should also be investigated.”
One focus of the work performed by Dr. Gary Potter, a consulting nutritionist and professor emeritus of equine science at Texas A & M University, was the best method of salt intake in horses. Potter now advises trainers of performance horses through his Potter Enterprises.
“There is a tremendous increase in the need for electrolytes in racehorses and performance horses due to both furosemide treatment (in some) and sweating (by all),” he said. “Trying to put enough salt in mixed feed to offset those loses is counterproductive because, when feed contains much more than 0.5 percent salt, horses tend to back off on consumption—which is the last thing you want in a racehorse or performance horse.”
Potter advises trainers to add 0.5 percent salt to the feed portion of the horse's diet, and offer an additional three ounces of loose salt daily — not mixed in the feed — during warmer weather to compensate for sodium lost in sweat.
“Horses in training, even in cooler/colder weather, will need some supplemental salt—one to two ounces daily,” he added. “If horses are fed salt in their stalls, it is much more workable to feed loose salt for two reasons: 1) the allocation and consumption of salt can be accurately managed and monitored, and 2) salt consumption due to salt craving can be prevented. Given free-choice access to salt blocks for horses in stalls frequently results in excessive salt consumption, excessive water consumption, wet, messy stalls, etc.”
Potter said Houpt's paper and other work points to an issue that often is mismanaged in performance horses.
“Clearly, horses given furosemide prior to a race or performance will become acutely dehydrated, and during a race or strenuous performance they will get hot,” he said. “So, the first thing they need following the race or performance is to get rehydrated and cooled off. Thus, they need to drink.”
He said horses should be permitted to drink as much water as they want when they come off the racetrack or complete a performance.
“The too-frequent practice of limiting water intake following a race or performance until a horse is ‘cool' is clearly contraindicated,” Potter said.
Australian Richard Butterworth has developed a way to get sodium into a horse via its respiratory system and skin by standing in a salt chamber for 15 minutes per day for three consecutive days. He presented his theory, which so far is unsupported by science, to the Horse Tech Conference in London on October 18.
Butterworth claims his Equine Salt Therapy rejuvenates cells, clears mucus, treats skin diseases, help wounds to heal, speeds up recovery from travel sickness, and reduces anxiety.
Leading Australian trainer Peter Moody was the first trainer to construct and use the salt chamber at his yard, and Australian veterinarian Christopher Elliott saw favorable results, Horse & Hound reported.
Butterworth is seeking researchers to study his Equine Salt Therapy. For now, he has only anecdotal reports of its benefits.
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