Your horse was diagnosed with equine protozoal myeloencephalitis, but with quick intervention by your veterinarian, careful administration of medications, and lots of nursing, he is on his way to recovery and being "cured" of the parasite. At that point, almost everyone has lots of well-intended advice on how to get your horse back to 100% fitness. There are a few nay-sayers who claim your horse will never be at full fitness again. Fact is, even the experts are divided about what percentage of horses can achieve compete-at-the-top rehabilitation.
As the horse begins to regain strength and coordination after basic ground work, exercise related to his discipline can be incorporated into his program. Care should be taken not to overtax the horse.
"Experience tells me that probably half, maybe 60%, go back and actively participate in their chosen area," says Frank Andrews, DVM, Diplomate ACVIM, Associate Professor and Section Chief of Large Animal Medicine, University of Tennessee. "Then there are horses that improve and become 100%. They do exactly what they are intended to do."
"Eighty percent of the horses I have rehabilitated are in full competitive work and have no limitations, whatsoever," reports Anne Stahl, a Northville, Mich., dressage trainer (Rosehill Farm) and FEI level dressage rider who has worked closely for nearly two decades with equine lameness specialist R.J. Keeran, DVM, on rehabilitating lame horses.
"I find that most horses remain neurologically unsound," states Michael J. Murray, DVM, Diplomate ACVIM, Associate Professor and Adelaide C. Riggs Chair in Equine Medicine, Virginia Tech. "Horses with neurologic deficits affecting their coordination and their ability to react appropriately to sudden changes are inherently more unsafe to ride than a sound horse. Sound horses can be risky enough, so add some degree of neurologic unsoundness and the chances for a catastrophic accident are increased. For these reasons, I refrain from recommending the use of a horse with neurologic deficits."
"Most horses can achieve significant if not full recovery with treatment and rehabilitation," says Stephen Reed, DVM, Diplomate ACVIM, Professor and Head of Equine Medicine and Surgery, The Ohio State University. "It is my opinion that about 25% of the affected horses will have some permanent deficits, but that only about 10% will be unable to exercise at all."
What these and other experts do agree on is the earlier treatment is introduced, the better the recovery. That goes for drugs and physical therapy.
Road To Recovery
The odds for a strong recovery depend upon how long the horse has been infected, where the damage occurred, the severity of the nerve damage, how much damage is irreparable, how much tissue is dysfunctional because of related inflammation and swelling, and how quickly treatment can be initiated.
"The earlier the horse is treated, the better chance that horse will respond and become normal again," says Andrews. "That’s because EPM is a progressive disease, although the progression can be halted and the horse can be cured. Protozoan parasites infect the inside of the nerve cells, and can actually kill the nerve cells as the parasite bursts open the cell and infects other cells."
Early intervention reduces spreading, and thus the damage, that these parasites can cause.
"But the longer the infection continues," Andrews warns, "the more risk of damage to the nervous system."
That damage could be permanent or temporary.
Explains Linda L. Blythe, DVM, PhD (neurology), Associate Dean for Academic and Student Affairs, Oregon State University, "If the protozoa kills the lower motor neuron that contains the axons that go to the skeletal muscle, that neuron is gone forever. One lower motor neuron cell may innervate 1,000 muscle cells; if that nerve dies, those muscle cells are left without innervation. Because the nerve is disconnected from the muscle it innervates, and the muscle doesn’t have a nerve supply, the muscle undergoes dramatic, neurogenic atrophy and loses half of its muscle mass in two weeks. If the parasite hits the brain’s neurons that tell the lower motor neurons what to do, the horse will become weakened and could develop paralysis, although it won’t get neurogenic atrophy."
Even when a neuron is killed, there is still hope for good muscle function. Says David E. Granstrom, DVM, PhD (Veterinary Parasitology), Assistant Director, Educational and Research Division, AVMA, author, Understanding EPM (The Horse Health Care Library), "There are more than enough neurons built into the nervous system. They operate in interconnected groups, so that if one neuron dies, the function it performed is not necessarily lost."
But Nature only provides a limited amount of time during which damage can be repaired or compensated.
"If the cell completely dies and those muscle cells don’t get a nerve supply back from adjacent nerves within a year, they will die and be gone forever," says Blythe. "But, there is something called axonal collateral sprouting, where if you have just partial injury where you’ve lost a few neurons but the other neurons that are supplying that muscle are still okay, then those neurons will send out part of their axons to kind of adopt these other muscle cells. By doing so, they can bring those muscle cells back."
This "sprouting" must be completed within a year.
"Muscle cells cannot live without nerve supply much past a year. They have to be reinnervated," says Blythe. "If a nerve is cut or demyelinates because of damage, and the axon kind of dies back, then regrows, the average regrowth rate is an inch a month. If you’ve got more than 12 inches to go, then everything within 11 inches will get reinnervated pretty well, as long as the nerve endings are together. But the portion that is 12 inches or more away, won’t. It can’t get there fast enough."
The best case scenario for the EPM horse is that a nerve has stopped functioning because it’s swollen or inflamed, but is not yet dead. Suppressing the offending organisms and eliminating edema and inflammation might allow the nerve to start functioning again. But, if a neuron has died, the best hope is that nearby nerves haven’t been damaged and will do collateral sprouting to adopt those muscle cells that have lost their nerve supplies.
Thus, the sooner treatment is started with anti-protozoal drugs (to suppress replication of the parasite), vitamin E (to promote the immune system and healing of nerve system tissue), and possibly non-steroidal anti-inflammatory drugs (to reduce inflammation), the longer the window of opportunity is open for restoration of nerve supply.
Once drug treatment is underway and the horse is showing some positive response, the next step is introducing rehabilitation.
Exercise benefits the recovering EPM horse. "Regardless of the cause," says OSU’s Reed, "the horse with a central nervous system disease will do better if allowed to exercise. Exercise can strengthen muscles, retrain damaged spinal tracts, and enhance healing of the nervous system."
Adds Granstrom, who for nine years conducted research on EPM as an Associate Professor of Veterinary Parasitology at the Gluck Equine Research Center, University of Kentucky, "Light work will help build the strength of innervated muscles during convalesence, but the ability of an individual to respond is dependent on the amount of innervation remaining and/or nerve fibers potentially available for recruitment to affected muscles."
Physical therapy can begin as early as two or three weeks after drug therapy has commenced, providing the horse is feeling well, showing positive response to treatment, and has some degree of stability or balance. You don’t want to lift the horse’s leg and have the horse fall over on you!
Exercise sessions might have to be brief at first. Says trainer Stahl, "Usually the horse is not in very good condition, so you may work with it for only five to 10 minutes a day. The horse benefits if you can do these exercises twice a day. They benefit from both physical and mental activity."
Reed says the program should be gradual and steady.
"It is not a good idea to work hard for two or three days, then take several days off. Rather, keep the horse in some short, daily exercise for several weeks to months, as the horse is able."
Take care not to overtax the horse.
"It is better to be patient and to avoid overworking the horse while it is on treatment," warns Granstrom. "At best, too much work too soon prolongs the length of time to full recovery and the return to normal activity. At worst, there will be an opportunity for a postmortem diagnosis."
Horses might take three, six, even 12 months to recoup maximum fitness and strength. The amount of rehabilitation needed will vary according to where damage has occurred and the severity of the damage.
The recovering EPM horse often is reschooled like a green horse, beginning with basic ground exercises. Andrews likes to begin longeing the horse to the left and right to improve strength in two 10-to 15-minute sessions a day, if the horse is able. Otherwise, do shorter sessions. Alternatively, a treadmill for the same length of time also builds strength. "If the horse seems to be improving, then increase the length of the exercise program," he says.
"We also recommend passive flexion and extension, depending on the horse," Andrews adds. "Picking up the leg and moving it forward and backward like a farrier would do."
Flexing the limb 10 to 15 times a day will help the joint stay flexible.
As the horse regains strength and coordination, Andrews suggests incorporating basic exercises related to the horse’s specific training.
"If the horse is a hunter or jumper, then start the horse doing ground jumping," suggests Andrews. "Even if the horse is an upper level jumper who was jumping five- and six-foot fences, start him on just poles on the ground. Then work up to poles just a few inches high, then up to one- and two-foot fences. Work him to where he’s feeling comfortable and gaining strength with the smaller fences."
Andrews also recommends working the horse in a saddle, but still without a rider, then adding weights to the saddle as strength increases. "That helps with developing muscle strength before you put the rider on."
Self-exercise is also beneficial, Andrews stresses. "We recommend pasture turnout whenever possible so the horse can develop coordination and compensation for his abnormalities. That way, if the horse is a little bit sore, they’re not going to overdo it, so it’s a self-limiting exercise. However, horses should not be turned out on pastures that are wet or the footing unsure, as a horse may fall and injure itself. Also, if the horse is severely uncoordinated or cannot maintain its balance, then turnout would be contraindicated."
When (if) the horse is judged stable enough to be ridden, Andrews recommends doing "very simple activities with the horse under very controlled circumstances. "Perhaps in a riding ring or small paddock, with somebody out there watching at all times just in case things get out of control. Take it very slow and build up strength by moving in circles, moving straight, and helping the horse build coordination."
Reed also recommends beginning with basic ground exercises consisting of hand-walking, ground poles, and cavallettis. Once the horse becomes reliable, Reed suggests ponying up hills and using dressage-type exercises.
Stahl, who’s spent a lot of time rehabilitating horses, employs a three-phase program in her recovery program. These exercises can be done mounted, if the horse is safe and strong enough. If the horse is unsafe because of lack of coordination, work the horse from the ground on the longe line using side reins so you don’t pull unequally on the neck.
Because the horse cannot always put his legs where he wants them, he can develop a lack of confidence in his ability to move and might appear resistant or reluctant to exercise, notes Stahl.
"The trainer should be very patient and compassionate during this period and hopefully, by developing the horse’s physical ability, will develop the horse’s confidence, as well," she adds.
The goal of phase one is to develop even rhythm, range of motion, and a workable balance.
"We use a series of exercises to increase range of motion and to encourage the horse to carry equal weight on all four limbs," says Stahl. Specific exercises will vary according to affected areas. "For example, in many horses, the right rear leg is affected where it will swing inward and shorter than the left rear leg. The rider puts the body of the horse in such a position that the horse is encouraged to move the right rear leg to the outside of his body and encouraged to swing the leg farther forward than he’s doing. Sit with your weight to the direction that you want the leg to go. Also, make sure you don’t block the rein on the side where you’re asking the horse to move forward."
In this phase, permit the horse to use his neck to balance.
If necessary, apply toe weights to help get the horse really to use his leg. "I put a toe weight on the leg that needs more weight to help it swing farther to develop the shoulder muscle in the horse," Stahl says.
At the beginning of this phase, the horse might be able to work for only five or 10 minutes before tiring. Gradually build up work sessions as the horse regains strength and until he is able to work comfortably for 30 minutes. Phase one generally lasts anywhere from a week to three months.
"You should see a more even rhythm and a horse that can manage a more workable balance," says Stahl. "Not necessarily an athletic balance yet, but the horse should appear even in the rhythm and can carry his balance and rhythm around turns and in circles."
Phase two works on getting the hind legs to carry more of the horse’s weight than the front legs. "We’re trying to move into a more competitive balance, like a dressage, jumping, or reining horse would need," Stahl says. "We work on shifting the horse’s weight from his front legs to his rear legs and forward again and back again. This should improve self-carriage, and the horse not only should have a working rhythm, but is really carrying himself completely.
"This phase requires a lot of transition work—trot and walk, canter and trot, canter and walk," notes Stahl. "At the same time, you’re still making sure that you further increase that horse’s range of motion with the affected leg with the phase one exercises."
This phase usually takes about three to six months to complete. The horse should be able to gradually increase workout time from 30 minutes to 45 minutes.
"The exercises should become easy for the horse," Stahl states. "The horse should be able to respond without appearing confused; then you can move on to phase three. But if the horse lacks determination in the swing of those legs, stay with the second phase."
In phase three, the horse is asked to shorten and lengthen his frame like a dressage, jumping, or reining horse. "We ask them to go forward in balance, shorten their frame, come back on their rear legs, then go forward again," says Stahl. "The difference from the second phase is they can now shorten and lengthen their frame to a greater extent. In this third phase, we work with range and control of motion, moving their haunches and shoulders anywhere you want them to be, and asking the horse to maintain this position."
This phase generally takes about six to 12 months. The horse should be able to gradually increase training sessions from 45 to 60 minutes. Once the horse has completed the program, employ these exercises as needed.
Stahl points out that the horse will achieve better rehabilitation if the trainer can target the areas that are weakened and develop exercises to strengthen specifically those areas. "You need to find someone who can assess the horse, almost daily," says Stahl. "You judge your exercise according to what you see that day. The veterinarian can help develop a program, but your trainer will have to continue the program with you."
Climbing On Board
Although ground exercises can develop strength, balance, and coordination, the million dollar question is how can you tell when or if the horse is safe to ride? Liability-conscious veterinarians are cautious about saying, "Yes, your horse is now safe to ride," and prefer to allow the trainer or knowledgeable rider to make that determination. Says Andrews, "We recommend that if a horse is severely debilitated, then riding it is out of the question. Putting a small kid on these kinds of horses is out of the question. If an experienced rider feels comfortable that the horse is ready to be ridden, then he or she has to make that decision on their own."
Indications that the horse might be stable enough to support a rider are that the horse seems strong after a workout and fairly balanced and coordinated. If in doubt, defer. Make sure your rehabilitation exercises build up strength in gradual stages: first the ground work, then the saddle, next the weighted saddle, finally the rider.
You also might want to have the horse re-evaluated.
"To help trainers and riders, we have the horses back very frequently to do neurologic exams," says Andrews. "We put the horse through a pretty rigorous battery of tests on the incline and walking on flat surfaces. We turn them in very tight circles. Walk them with their head elevated. We also do placement and tail-pulling types of things to give us an idea of how strong the horse might be. This can help the client and trainer involved with the horse."
Keep in mind, too, that the horse can suffer a relapse, although Stahl has observed that relapses are less likely to occur in horses which were diagnosed and treated promptly.
Along with physical therapy, adjunctive alternative therapies also can be helpful in relieving muscle aches. Says Granstrom, "Some alternative therapies, appropriately administered, seem to help sore horses feel better. Because asymmetric ataxia can produce soreness and injury, these therapies should be helpful. None of these methods eliminate parasites by themselves, but they can serve as a useful adjunct to standard therapy."
Reed also recommends alternative treatments. "We feel hydrotherapy is very, very effective in increasing blood supply to the muscle. We’ll use hydrotherapy two or three times a day for 10 to 15 minutes each time."
He says that deep massage, acupuncture by a trained veterinary acupuncturist, and therapeutic ultrasound can be helpful. Although he does not directly perform any of these procedures, many of the horses which are recovering from neurologic diseases appear to benefit from some of these methods.
"They may help horses that developed muscle soreness in trying to compensate for various disabilities," notes Reed. "Acupuncture has been reported to decrease pain and allow horses to function quite normally for a period of time."
He notes that some clients find strategically placed magnets helpful by supposed improvement of blood flow to various muscle groups and the skin. However, he points out there are no controlled studies that demonstrate their benefits.
One device that has generated enthusiasm is Theraquine FES. Says Blythe, "This new product is probably the best one I’ve seen on the market to date. Essentially, Theraquine uses an electrical stimulus that mimics the motor nerve activity that would be coming to those muscles. It sends an electrical impulse into the nerves that mimics as if the nerves were functioning themselves—like an artificial nerve stimulator. It helps exercise the muscle fibers that are there, strengthening them, thereby strengthening the horse. It essentially makes the muscles contract. But if the muscle has totally lost its nerve supply because the neuron is dead, then there’s not much you can do for that nerve fiber unless another axon will come over and adopt it. But you are strengthening the muscle fibers that still have partial nerve supply."
Blythe notes that this same technology has been used on humans. "The company has a good history of using this on human paraplegics. In fact, Christopher Reeve is one of the people they work with to try to keep those muscles functioning."
Stahl has found that the use of a neck cradle in horses which have weaknesses in the neck area is very helpful. "We don’t want the horse to swing his neck uncontrollably or whip his neck around like he’d go for a fly, side to side. Up and down and turning of the head is normal and needs to be allowed."
She feels that except when the horse is being ridden or longed, the afflicted horse should wear the neck cradle 24 hours a day. To keep the horse comfortable, Stahl customizes the cradle for each horse. "That’s an important part," she says. "Many times the underside of the cradle is too long and that makes the horse stand in an uncomfortable position. But if you adjust it to fit the horse comfortably, he will be okay."
She says that most horses with weakened neck areas can be out of the neck cradle within three to 12 months.
The final component in rehabilitating the horse is putting together a team of people to help the EPM horse. "This is a managed care program," says Stahl. "You need involvement not only from the owner and trainer, but from barn staff, veterinarian, and farrier. It’s going to take all of these people to manage the recovering EPM horse."
The trainer needs to assess the horse’s weaknesses and adjust its exercise program accordingly.
The veterinarian needs to keep an eye on medical management and help develop the physical therapy program.
Barn staff need to be alert to changes in the horse or to help with equipment.
"EPM horses have many secondary problems that arise from the condition and treatment," says Stahl. "These have to be watched and carefully tended to. For example, we had an EPM horse here that had very dropped suspensories, so the horse had to wear supportive boots in the stall. These boots had to be managed by barn staff. You couldn’t just ignore those boots for the day; you had to make sure he was comfortable in them and they didn’t shift.
"Another horse, as he improved, began kicking at the wall of the stall, probably because he was starting to get some sensation back in his leg and it felt tingly or unusual. So we put carpet on the wall to keep the horse from hurting himself."
Barn staff need to keep an eye on how the horse eats, as sometimes drug therapy can cause inappetence. They also need to be conscientious of how long a horse can be turned out.
The farrier needs to adjust shoeing and trimming to enhance stability and evenness. "The shoeing is very important," says Stahl. "These affected legs don’t go exactly where the rider wants them to go until the horse is recovered. Often, one leg will hit another or the foot can forge or interfere, and the farrier can really help with this."
The farrier can adjust the tip or the trim of the horse behind so that the leg will have a little more clearance right to left, left to right. He or she might deal with a forging problem by trimming or rounding the toes in the front, letting the horse break over more quickly, or stubbing the horse off behind to keep him from coming up and hitting his front leg when he goes.
"Obviously," says Stahl, "the main improvement will come when the horse can control the leg better, but in the meantime, the farrier can really help you keep the horse from hurting himself while he is learning to use himself properly again.
Will the time and money and rehabilitative effort you spend working on your horse’s recovery eventually pay off? The answer is a definite maybe. But the effort put into a rehabilitation program might make the difference in whether your horse comes back to his former athletic form.
About the Author
Marcia King is an award-winning freelance writer based in Ohio who specializes in equine, canine, and feline veterinary topics. She's schooled in hunt seat, dressage, and Western pleasure.
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