What's Up with Wobblers?
- Nov 1, 2011
Photo: Stephanie L. Church, Editor-in-Chief
It used to be that veterinarians automatically recommended euthanasia when they diagnosed horses with wobbler syndrome, a disorder affecting the musculoskeletal and neurologic systems that can upend an affected animal's prospect for a quality life. Today, thanks to new and continuing research, many wobblers can be managed and some can even go on to become safe riding horses.
A horse with wobbler syndrome (also called cervical vertebral stenotic myelopathy) suffers from narrowing of the spinal canal that pinches/compresses his spinal cord as he grows. The trademark clinical signs of a wobbler: He's incoordinated (exhibits ataxia) and lacks an awareness of where his limbs are in space (proprioceptive deficits). Although many neurologic conditions can cause ataxia, if a once-thriving colt becomes hopelessly incoordinated, for example, he could be a wobbler.
"It is important for owners and trainers to realize that something can be done for these horses, and early diagnosis is the key to staying alive," says Barrie Grant, DVM, MS, Dipl. ACVS, MRCVS, who has a consulting practice in Bonsall, Calif.
Although wobbler syndrome seems to appear in horses unexpectedly, there often are subtle signs of the condition that were missed. "Occasionally, you can have an acute onset. One day the horse is fine, and the next day he is not," says Stephen M. Reed, DVM, Dipl. ACVIM, an associate at Rood & Riddle Equine Hospital in Lexington, Ky. "Most of the time, you see a progressive onset of clumsiness--meaning weakness (knuckling, stumbling, dropping, or dragging of the limbs); ataxia (specifically, abnormal swaying of the limbs in the air as the horse walks); pacing (both legs on the same side stride together in nonpacing horses); and truncal sway or spasticity (the horse looks like a tin solder when he walks). That is what people see. There is no evidence of brain problems, the horse is mentally alert, he is 'with it,' and he looks right at you. He acts right and eats normally, but he has some clumsiness when he walks."
Most people don't recognize these subtle signs until they become prominent--and more difficult to treat. Sometimes horses are already training for a performance career before issues arise, and as the condition progresses they just refuse to work.
"They don't want to go over a jump because they don't know where their legs are," Grant says. "But they do it for a long time for their owners, because horses try and do extraordinary things for their owners.
"The acute signs bring wobblers to people's attention," he continues, "but when you talk to (owners) they tell you, 'The horse would always stand still in the pasture when the other colts ran around. He always acted a little clumsy.' "
Any breed can suffer from wobbler syndrome, but it tends to be more common among Thoroughbreds, Quarter Horses, and Warmbloods and also tends to occur in younger horses (within the first year or two of life), according to Jennifer Janes, DVM, a graduate student in the University of Kentucky's (UK) Department of Veterinary Science. However, senior horses with arthritis can develop the disease as well.
According to James N. MacLeod, VMD, PhD, John and Elizabeth Knight Chair and professor of veterinary science at UK's Gluck Equine Research Center, in Lexington, colts and young stallions are at least three times more likely to have wobbler syndrome than fillies and mares, and some researchers think certain horses might have a genetic predisposition toward developing the disease.
"The male predisposition is clear," says MacLeod, "but we don't know the specific reason for the gender difference."
Currently, MacLeod, Janes, and their colleagues are trying to establish if ¬specific genes or genetic determinants contribute to the development and progression of this disease. "There are conflicting data in the literature," MacLeod says. "We are trying to address this question that has been around for many decades with the new tools available since the sequencing of the equine genome."
The research team is collecting DNA samples and comparing genetic markers from horses with wobbler syndrome to those of healthy horses. "This is the same technology that researchers use to see which people are predisposed to different types of cancer and other health conditions," MacLeod says. "We are looking for an association between a genetic marker or multiple markers and wobbler syndrome."
If they find an association, they can use other genetic tests to determine the strength of that association and whether there is a gene in that marker's area that contributes to or causes the disease or its progression.
Another important contributor to wobbler syndrome could be rapid growth. This might be one reason why more young males experience the disease than females--they tend to grow faster, according to Reed. "The gender differences could be due to the rate of growth, how fast they grow, how big they grow, or growth hormones," he explains. "If you have an animal with the ability to grow rapidly to a large size, and you feed the animal so it can grow at a rapidly excessive rate, and you don't have impeccable balance among major nutrients like calcium, phosphorus, and the trace nutrients copper, zinc, and manganese, the animal might not be able to lay down and calcify bone in a normal way."
Reed says trauma also can lead to manifestations of the disease, particularly in a horse with a narrow spinal canal. "Wobblers does not require serious trauma (to develop)," he says, explaining that roughhousing sometimes is all it takes. "There can be trauma when colts and fillies play. They rear up on each other. They arch their necks. They do all kinds of things when they play, and those are all potential (opportunities) for injury."
Is It Preventable?
Veterinarians who suspect horses have wobbler syndrome usually perform standing radiographs (X rays) of the neck (cervical vertebrae) to assess whether the canal is narrowed or the spinal cord compressed. They might also suggest a myelogram, in which they inject a contrast dye around the spinal cord before taking radiographs. This compression can occur in more than one place, says Grant, and the contrast dye reveals where any pinching exists.
Magnetic resonance imaging (MRI) and computed tomography scans also would be excellent detection tools, but these instruments are not built to accommodate the horse's neck.
Some researchers and veterinarians have seen and treated many wobbler cases--enough that they can look at a radiograph of a foal's neck and predict whether he is predisposed to develop the disease. If there are early signs that the canal might be narrowing, owners can take steps early on (e.g., through adjusting diet and other management approaches) to reduce this risk.
For instance, as part of a study in the early '90s, William J. Donawick, DVM, professor emeritus at the University of Pennsylvania School of Veterinary Medicine, and his colleagues took standing radiographs of the cervical spines (necks) of foals on one farm to assess whether any of their vertebral canals might ultimately narrow too much, leading to wobbler syndrome. Through this evaluation they identified 18 offspring with the potential to become wobblers. They confined these foals so they would not suffer trauma while roughhousing in the pasture and fed them low-protein, low-energy diets that helped slow their growth rates. By 17 months of age, all but one horse sported normal vertebral canals and showed few to no signs of wobbler syndrome.
While many consider this corrective method to be extreme, Grant acknowledges that closely managing a young horse on the farm might reduce his chances of becoming a wobbler. "If drastic changes of the diet are made in (horses) less than a year of age, sometimes you can prevent the problem," he says. "After a year it is very hard to change the configuration of the bones and take the pressure off the cord by changing the diet."
In a 1994 study that appeared in the American Journal of Veterinary Research, Bonnie R. Rush, DVM, MS, Dipl. ACVIM, professor of equine internal medicine at Kansas State University, determined that if a veterinarian measures the height of the canal and compares it to the height of the vertebral body, about 80% of the time he or she can predict whether a horse's spinal canal is too small.
"If you identify (a potential wobbler) younger than 10 months of age, you can do dietary restrictions or dietary modifications, along with careful exercise and anti-inflammatory medications like steroids, to reduce inflammation of the spinal cord and see if you can get the spinal cord to heal," Grant says.
Because wobbler syndrome might have a genetic component, keep a close eye on foals if you're a breeder. Have your veterinarian perform baseline radiographs on young foals and conduct periodic neurologic exams, and be vigilant about watching for the previously mentioned signs of clumsiness or weakness that can go unnoticed. If a broodmare has one wobbler foal, Reed suggests owners monitor her subsequent foals closely for neurologic signs.
"It is not hard to do a little neurologic exam on your horses from time to time," says Grant, who recommends owners perform the following easy tests to bring to light any neurologic issues, particularly in growing horses:
- Put pressure on the horse's back and see if it gives, which might indicate a neurologic issue.
- Pull his tail to each side and see if you can "pull him over" easily. He should be able to resist you.
- Back him up and see if he drags his toes or pauses before backing up. (In the latter case he might be trying to figure out where his hind legs are.)
- Turn the horse in a tight circle; if he swings an outside leg wide out of control or pivots on the inside forelimb, that could be an indicator of a problem.
- Pass one forelimb over the other, set it down, and see how long it takes for the horse to uncross the leg--the quicker the better.
"One of these signs alone does not tell you a horse has wobblers, but a combination of these signs is cause for concern," Grant says. Record a video of yourself or someone else doing these tests every three months for a foal's first year and then compare them or ask your veterinarian to review the videos.
What Can be Done?
Veterinary surgeons have developed a surgical technique that involves drilling a hole between the compressed vertebrae of the spine from underneath the neck and inserting a steel implant called a Bagby basket. This implant fuses and immobilizes the spine, says Reed.
"We think about 80% of the horses will improve with surgery," Reed explains. "About 65% can go on to be athletes at their original intended use. Others will improve enough to have some limited activity."
Surgery and rehab are viable options, but they are costly. Depending on where you live and the veterinarian who performs the surgery, surgical treatment can cost $7,000-$10,000--and there's no guarantee horse will recover. The real rub is that nervous tissue heals slowly, so it might take a year before the owner truly finds out how the horse fared--another reason why many owners might choose to euthanize the horse instead.
"Because this is a serious problem and can be devastating, many people just give up before they even think about trying to treat a horse with wobblers," says Reed. "We've learned there are many things we can do to help these horses. I would hope that people would not give up before they even find out what they can do."
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