On December 26, Canadian champion grass horse Conquest Enforcer was euthanized due to complications from a bladder stone. After finishing last in the Grade 3 Red Bank Stakes three months earlier, Conquest Enforcer was back in training in Florida when veterinarians took the 5-year-old horse into surgery to resolve a problem with his urinary flow. John Guarnere, owner of Imaginary Stables, told followers via Twitter: “They discovered a hole in his bladder and decided it was humane with the pain and lack of a normal life to put him to rest.”
Dr. Claude Ragle, a professor and surgeon at Washington State University who has been involved in five studies on the subject, was asked to explain why a seemingly routine surgery had such a sad outcome. Ragle said bladder surgery in small animals and humans is routine, but it presents a problem for horses.
“It's very difficult to access the horse's bladder surgically by open, normal methods,” he said. “The bladder is almost unreachable. The best access to the bladder is when we use minimally invasive techniques — laparoscopy — so that is how best to repair it, but it depends on the quality of tissue.”
Ragle said the anatomy of male horses — the long, narrow urethra — makes surgery more complicated for them, even using laparoscopy, than for females. Furthermore, patching a hole in a horse's bladder with tissue from the patient's intestine, as is done in small animals and humans, may not be possible in a horse. If a urinary obstruction has caused excessive tension on the bladder tissue or disrupts the blood supply to part of the bladder, the tissue can lose its integrity.
“Bladder tissue will heal well, but if the tissue is compromised from excessive tension or poor blood supply, then it's very difficult to recreate a new bladder out of other tissue,” Ragle said.
Bladder stones in horses can be as large as a human fist, requiring surgeons to break it up into small pieces that can be removed using an instrument and a retrieval pouch. But Ragle said marble-size stones can be more dangerous.
“They block the ability of the urine to come out and sometimes before you realize it, the bladder is getting so large you can end up with secondary problems from the pressure,” he said.
Ragle described bladder stones as “an older-horse disease,” and he said its occurrence in a 5-year-old stallion is unusual. In general, bladder stones are rare in horses because a horse's body is designed to excrete excessive calcium through the kidneys. Any breakdown in the physiology or anatomy that normally protects a horse from getting a bladder stone could make that individual prone for recurrence of the problem.
Is diet to blame?
In humans, urinary stones usually are attributed to a faulty diet and not consuming enough liquid to adequately flush calcium from the system. The horse's physiology is very different from humans, said Dr. Joe Pagan, nutritionist and president of Kentucky Equine Research in Versailles. He believes an underlying problem probably is the cause, such as damage to or infection of the urinary tract. The underlying issue doesn't allow the horse to void urine as efficiently as normal horses, which might attribute to the fairly high recurrence rate.
“There are huge numbers of horses that live on nothing but alfalfa hay, and they're ingesting massive amounts of calcium in that alfalfa, and you never hear of bladder stones,” he said. “In 35 years as a nutrition consultant, I've never been asked to do something for a horse that had this problem. Having said that, I know it happens, but it's rare.
“Stones occur when you have the urine fairly saturated with calcium carbonate and the pH is high and the bladder or urethra or any of the plumbing is somehow not allowing it to be adequately voided. Then the calcium will crystalize and form into a stone. If that happens, it's a serious problem and the chances of recurrence are very high. That tells you there is something else going on that created the situation to begin with. Modifying the diet alone does not necessarily get rid of it.”
Pagan is concerned that owners with normal horses may overreact to news of Conquest Enforcer's death by decreasing the amount of calcium in their horses' diets. In racehorses especially, this could deprive them of the calcium they need to repair microfractures caused by performance.
“For horses that have not expressed those types of problems, you want to encourage water intake and large volumes of urine,” he advised. “There are two ways you do that. One is by providing them more electrolytes and sodium primarily. … The second is that water intake is highly coordinated with fiber intake. So if you can get a horse to eat hay and give it access to water, it will drink more water. And if it drinks more water, it's going to void more urine, which means the urine will be more dilute and less likely to crystalize.”
For horses that have produced urinary stones, Pagan said reducing calcium intake must be done gradually, with emphasis on maintaining a proper ratio of calcium to phosphorus (between 1:1 and 2:1). As in normal horses, encourage consumption of water by adding electrolytes, primarily salt, to the diet. But decreasing the pH of the urine to make it more acidic so it dissolves stones is difficult in horses. This typically is attempted by supplementing the diet with an additive used in dairy cattle, but the additive is unpalatable and horses typically won't eat it.
“The take-home here is that this is a fairly rare problem,” Pagan said. “It's not something that's happening to every other horse. What worries me is that people may take extremes trying to prevent something that is not that common and screw up their horse by withholding calcium.”
Dr. Thomas Divers, professor of veterinary internal medicine at Cornell University, described in the Merck Veterinary Manual the symptoms horsemen should look for if they are concerned a horse might have a stone blocking its urinary tract.
“Affected horses frequently stretch out to urinate and may maintain this posture for variable periods before and after micturition. Additional signs may include scalding of the perineum in females or of the medial aspect of the hindlimbs in males. Geldings and stallions may protrude the penis flaccidly for prolonged periods while intermittently dribbling urine. Affected horses may occasionally exhibit recurrent bouts of colic or an altered hindlimb gait.”
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