Studies shed insight on a common affliction
story by Hope Ellis-Ashburn
Twenty minutes into her daily jog, a Standardbred filly developed a short, stiff stride behind. Breathing harder than her level of exercise indicated, she was sweating profusely and was reluctant to move forward. After climbing out of the jog cart, her driver ran his hand over her croup and loin and found that her muscles were abnormally firm to the touch. Following repeated occurrences in the days ahead, blood tests would reveal that the filly had developed a condition commonly known as tying up.
Tying Up Explained
Stephanie Valberg, DVM, PhD, Dipl. ACVIM, ACVSMR, of Michigan State University’s (MSU) McPhail Equine Performance Center in East Lansing, recently completed an extensive study on this condition. She said that a Swedish study showed that about 6.6 percent of Standardbred trotters suffer from it.
“The term tying up is just like the term colic. It’s a general descriptor of horses that are developing muscle pain,” Dr. Valberg explained. “It should specifically be used for horses that are developing muscle pain that is associated with muscle damage.”
That muscle damage is determined by taking a blood sample that shows increases in two blood proteins that leak out of the muscle and get into the bloodstream as the muscle cells are damaged.
The proteins measured are CK (creatine kinase) and AST (aspartate aminotransferase).
The presence or absence of the proteins in the blood work is vital to determining the true cause of cramping.
“The blood test is important, because horses can develop cramping, just like we develop cramping, that is painful,” said Dr. Valberg. “Both tying up and cramping look the same. The difference with tying up is that you are going to have damage to the muscle that you can confirm with a blood sample. Then, you’ve got some specific things that you can look at that are different from what is causing muscle cramping.
“Standardbreds can tie up for sporadic reasons that aren’t connected to permanent underlying susceptibility to tying up, or for chronic reasons described as recurrent exertional rhabdomyolysis (RER), the clinical term for repeated tying up.
“We don’t call it recurrent exertional rhabdomyolysis until they’ve had two or three episodes.”
Though it can affect both genders, about 60 percent of affected Standardbreds are fillies. It’s most commonly seen in horses that are between 2 and 3 years of age as compared to older horses. While older horses can develop tying up, it is much more common when they are younger. Typically, those horses who develop the condition have a more nervous temperament.
“Or, they’ll be really strong and on the muscle when you’re driving or exercising them,” said Dr. Valberg. “They’ll be wanting to go. Temperament is more often associated with tying up than not. There’s a strong association with developing tying up and being under high-stress, excitable circumstances.”
Genes and Evolution
In some horse breeds there is a known genetic component, but studies show that there is not one single gene linked to tying up in Standardbreds.
“There have not been a lot of studies done on the Standardbred breed, but from what we know the most common form of tying up for them is stress associated,” said Dr. Valberg.
“What we think is going on is there may be a familial predisposition linked to a number of genes that have a small effect on whether horses develop RER, but it’s not because there’s one gene with a major effect and if you inherit the abnormality in this gene, you’re getting the disease.
“There may be multiple factors in the horse’s genetic background that can contribute to its being susceptible. Then there’s the very strong influence of the environment and the stress of the environment on how the muscle functions. Those combinations of factors tip the horse over the edge.
“What we think happens with tying up is that horses have evolved so that they are incredible athletes. Their muscles have evolved very specific attributes that make them able to have a lot of power in their muscles that makes them go really quickly.
“Those adaptations involve the way that they start and finish a contraction of the muscle, and that involves being able to store calcium inside the muscle in these little storage stacks. Then, when you want the muscle to contract, they release that calcium. It interacts with the contraction or proteins and allows the proteins to slide and shorten the muscle. They very quickly have to pump that calcium back into those storage stacks so the muscle can relax and get that next contraction.”
It seems that changes in the muscle occur in horses with RER who are in stressful environments.
“We think they release much more calcium than they should, at that point in time, and it can’t get pumped back fast enough,” said Dr. Valberg. “This triggers damage to the cell so that the muscle starts to break down. If you have enough of the muscle cells do that, then you develop all of those drastic clinical signs of tying up.
“The muscle cells manage their calcium concentrations independently from blood calcium concentrations. The calcium involved in muscle contraction has nothing to do with the amount of calcium that you are feeding them in their diet or that is in their blood stream, but everything to do with how they move it from storage sites to the contractile proteins in the cell.”
The first step once a horse has been diagnosed with tying up is to become aware of the role that stress plays.
“Change the management strategies for the horse, make them as comfortable as possible, and drop their excitement and stress levels,” Valberg said. “We know from the studies that Standardbreds are most susceptible to developing tying up when they’re jogging for more than 20 minutes or so. The first thing we recommend is to break up the jogging miles so that you don’t do 40 minutes at a time.”
Instead, if 40 minutes is the goal, Dr. Valberg recommends 20 minutes in the morning and 20 minutes in the afternoon. She also recommends closely observing the horse in the stable environment to see whether or not the horse seems to prefer to exercise first or last, would prefer to be located beside a horse that it likes, or moved to the back of the barn instead of the front. Small changes that will eventually make a horse happier can be key to halting or slowing the re-occurrence of the condition.
Some success has been seen in changing a horse’s environment altogether, such as returning the horse to the farm, then bringing it into train or race followed by a return to the farm for turn-out. Turn-out every day for susceptible horses can make a big difference.
Diet also plays a role. Dr. Valberg said that horses on a high-grain diet are much more likely to tie up because it increases their level of excitement. She added that some studies have shown that if you decrease the amount of starch and sugar in the diet and increase the amount of fat to keep the calories they need, it will prevent a lot of tying up episodes.
Some medications can be used that affect calcium regulation in the muscles. Dantrolene, for example, can be administered about 60 minutes before exercise. However, the medication must be withdrawn from the horse before any racing or competition takes place. Check with your veterinarian about withdrawal times. Even though it can’t be used in competition, its use in training is a small step in preventing a horse from reaching a certain threshold and developing clinically harmful signs to the extent possible.
Concerning diet, Dr. Valberg added that several feed supplements are being offered to help prevent tying up in horses.
“We worked with Kentucky Equine Research and Hallway Feeds to develop a feed called ReLeve that was shown in published studies to decrease tying up in Thoroughbreds,” she said.
“Feeding lower-starch, fat-supplemented diets can be a benefit, but I always tell people, if they found a formula that seems to work for their horse, and it’s stopping it from tying up, then I wouldn’t change what you are doing. Don’t change what works for you.”
In the long run, even if diet, exercise, environment and management strategies don’t prove to be entirely helpful, the horse’s career may not be over.
“What was kind of interesting is that in a study that was performed in Sweden with trotters, they looked at the performance records of the horses that tied up and compared them with the records of the horses that don’t,” said Dr. Valberg. “The performance of the horses that tied up was statistically better than the ones that didn’t. That may be because of an underlying condition. If you can manage it, it might give them a little better muscle contraction speed.”
If additional management strategies are needed beyond those previously recommended, Dr. Valberg offered that owners of affected horses may utilize racing every second week, to decrease stress, allowing them to use Dantrolene in training, and removing full days off from the training schedule.
“Standing in a stall predisposes horses to tying up,” said Dr. Valberg. “On a rest day, take them out and move them around a little bit for about 10 minutes, or put them on a walker, or provide turnout.”
Dr. Valberg hopes that in the long run, additional studies on dietary and other management practices may shed more light on tying up. Following up on a study supported by the USTA, she is working together with Dr. Joe Pagan at Kentucky Equine Research on a new nutritional approach.
For now, she said, “If we can get some of these horses through getting used to being at a training facility, getting used to all of the newness of racing, and the newness of being there, and manage them so that their stress levels drop, and ensure they are not on a high-starch diet, some of these horses will have much less frequent episodes of tying up or very infrequent to no episodes.”
While there will always be particularly difficult horses having repeated episodes of tying up and being difficult to manage, the overall prognosis is good even if it means that over the long-term, they go on to second careers in lower-stress environments. HB
Hope Ellis-Ashburn is a freelance writer living in Tennessee. To comment on this story, email us at firstname.lastname@example.org.
Put On A Show
Even the great ones can suffer from tying up
Although she won many of the sport’s top races for pacing females, earning $2.4 million, Put On A Show battled tying up. Her trainer, Chris Ryder, luckily came up with a plan for managing her that largely kept the episodes at bay throughout her career.
“The more she was locked up in a stall, the more she tied up,” said Ryder. “I kept her outside in the field as much as possible. She had to be out in the field before she did her work.”
While Ryder did a little bit of what’s known to help, such as turning the filly out in the field, he also put her on a unique exercise routine.
“What worked for me is you only jog them slow a couple of laps, then turn them and go a half-mile and go in 1:10,” shared Ryder. “Only go a half. Don’t go a mile. You don’t want to get them tired. The time on the track compounds the problem.
“My theory is also that if you stretch them out a little every day, it keeps their muscles loose. But the key is to not keep them on the track too long. They only tie up on the racetrack, so you don’t want to be on the track too long.”
Ryder also said he learned from the late Canadian horseman Bill Robinson that regularly feeding baking soda would help horses that tie up.
“I feed two to three ounces of baking soda in their feed, but not on race day,” he said.
While Ryder kept Put On A Show on a strict routine when she was at home, detention and traveling tipped her into an episode of tying up, most notably when she raced at the Red Mile and was upset in the Glen Garnsey Memorial.
Ryder agrees with the theory that weather can cause a tying up episode, and he also follows recommendations for keeping horses hydrated and with plenty of electrolytes. Although Put On A Show last raced nine years ago, Ryder said he still follows the plan he adopted with her to combat tying up.
“I can explain my process and thinking about tying up to people that have horses that tie up and they won’t do it. They would rather just let the vet treat the horse,” he said. “Also, people think that training every day is hard on them. But tying up is what is hard on them, not the half-mile in 1:10. You have to prevent the tying up. Tying up is so painful and does so much damage. The more comfortable they are, the happier they are to do their work.”