Muscle biopsy could indicate whether horse is physically suited for racing

by Denise Steffanus

DID YOU ever wish a fortune teller could spread the cards in front of you and divine if your racing prospect will be a worthwhile investment of time and money? Cross the gypsy's palm with silver, and she will entertain you and indulge your fantasies of roses, black-eyed Susans, and carnations. But science may have the real answer.

Research in Germany, Sweden, and Spain has sought to determine if certain horses are more adaptable to particular disciplines by sampling the types of fibers that are predominant in specific muscles in the horse's body. A study of German Warmbloods found that horses specifically bred for show jumping had inherited a majority of muscle fibers that enabled them to generate enormous power in the hindquarters to take off for a jump, while horses bred for dressage naturally had more of the type of muscle fibers that allowed them to perform at low intensity over a long duration.

That same technology can be applied to determine if a racing prospect has inherited the physical ability to perform well or if the horse will have to rely on heart to triumph over his shortcomings. A simple muscle biopsy could hold the answer.

Different muscle fibers

Muscle fibers are divided into two major types and one adaptive type. Fiber types are classified by how quickly they contract and relax, a cycle called a "twitch."

Slow-twitch fibers, Type I

•Contract and relax slowly;

•Use large amounts of oxygen to produce energy (aerobic);

•Appear reddish because of their rich blood supply; and

•Are long and thin to facilitate nutrient flow and waste removal.

Fast-twitch fibers, Type IIB

•Contract and relax quickly;

•Produce energy primarily without using oxygen (anaerobic);

•Rely on carbohydrates for fuel;

•Are pale in color because they require less blood supply; and

•Are larger in size.

Fast-twitch oxidative/glycolitic fibers, Type IIA

•Contract and relax quickly;

•Are capable of anaerobic or aerobic function, depending on what type of exercise they are recruited to perform; and

•Respond to training to develop more anaerobic or aerobic capacity.

Thoroughbreds have more slow-twitch fibers than heavier breeds, largely because of genetics and selective breeding. They also possess a greater proportion of Type IIA adaptive fibers. The predominance of these two types of fibers provides the Thoroughbred with speed and staying power.

Muscle biopsy

Monica Aleman, D.V.M., Ph.D., is director of the Neuromuscular Disease Laboratory at the Center for Equine Health at the University of California at Davis. According to Aleman, performing a muscle biopsy on a racing prospect can be helpful in determining that horse's athletic potential.

"It's complicated," she said. "A muscle biopsy will be helpful. However, it won't have all the answers if you just want to know whether a horse would be a good performer or not, because there are several issues that are associated with successful racing."

Just because a Thoroughbred has the correct proportion of the fiber types that are desirable in a good racehorse does not mean the horse will excel, she said. Many factors must converge to produce a successful racing career, such as the trainer's expertise, appropriate conditioning, proper nutrition, good husbandry, will to win, and luck.

On the other hand, a horse that does not inherit the proper muscle type for his profession will be fighting an uphill battle, as will his trainer.

"[Training a horse with improper muscle type] wouldn't necessarily be a waste of time, because you can do a little bit of switching the metabolism of the fibers by training," Aleman said. Muscles can be trained to perform a specific task by recruiting adaptive Type IIA fibers to help with those duties.

"However," she continued, "if you see too many of IIB fibers, for example, in that horse's muscle, you won't be able to change 100% of [the muscle] because there are also genetics involved, breeding, and a lot of other things in the fiber type. But you can definitely make some switches by training."

The Swedish study was performed on heavier breeds, but Aleman said she believes the principles of that study also could be applied to Thoroughbreds to determine innate ability.

"Yes, absolutely. That can be done," she said. "Basically, what they did in Sweden is a simple procedure of taking a muscle biopsy, and by doing certain reactions with that muscle, you can tell what fiber type they have. You can't give any guarantee, but just by looking at the fiber-type distribution of the muscle of that horse, you can tell that this horse probably has all the chances to perform well, based on the fiber-type distribution."

The procedure

A muscle biopsy is a minor surgical procedure whereby a small piece of muscle, usually the gluteal muscle, is extracted from the horse through an inch-long incision in the skin and subjected to several laboratory tests. After the surgeon makes the incision, he or she will go in with a scalpel and scissors to get the muscle sample. Other ways of performing a biopsy are by means of a skin-punch needle, which is gently inserted and rotated to extract a small piece of muscle tissue, or by using a Bergstrom biopsy needle for deeper sampling.

"We usually take about one centimeter by one centimeter of muscle tissue, which is not a lot for a horse," Aleman said. "Skin-punch biopsies are different sizes. It goes from two millimeters to eight millimeters. Normally, to take a good sample, I prefer the larger one. Eight millimeters by eight millimeters is still very small for the horse."

After the procedure, the surgeon closes the incision with just one suture so the biopsy does not leave a noticeable blemish once the incision heals, which takes about ten days. During those ten days, the horse should get only mild exercise.

"What we say is do not heavily exercise the horse while it heals, basically until we remove the suture, which is about ten days," Aleman said. "This doesn't mean the horse has to be completely confined in a stall. The horse can move and do very mild exercise, but I wouldn't race the horse in those ten days."

In the laboratory, trained technicians inspect the form and structure of the cells to see if they look normal.

"We do 13 different reactions with this muscle to check for enzymes, to check for sugar in the muscle and different organelles, little organs of each individual muscle fiber," Aleman said. One essential organelle type is mitochondria, which utilizes oxygen in the tissues to produce energy.

"We do all kinds of things," Aleman said. "So it's pretty extensive. We just investigate whether the muscle is normal or not."

Muscle biopsies also are useful as part of an overall workup to determine the cause of poor performance in a horse that is in training or currently is racing.

"If you have, for example, an unfit horse, that unfit horse will have maybe more of one certain type of muscle fibers versus another one," Aleman said. "An unfit horse might have more type IIB fibers. Of course, if you see a lot of type IIB fibers in a horse that is supposed to be a good racer, you can tell that horse is not fit enough. And you can tell that the horse is not going to be doing well in a race."

For horses that are not performing well, UC-Davis offers diagnostic services through its Equine Athletic Performance Laboratory, under the direction of James Jones, D.V.M., Ph.D., professor and chair of the Department of Surgical and Radiological Sciences. In the laboratory, clinicians perform an array of diagnostic tests on horses exercising on high-speed treadmills to determine abnormalities that may be causing poor performance. Looking more closely at how the horse's muscles function is a key component of the workup.

"There are certain gross changes that if we saw those in a muscle biopsy, they would be useful, and in particular if we've seen this before in horses that have had some performance problems," Jones said.

One essential finding that might be revealed by a muscle biopsy is that one of the enzymes in the muscle is malformed and not functioning properly.

"You couldn't tell unless you actually went into those muscle fibers, did the sampling, and then evaluated how those enzymes were functioning," he said. "[Without a biopsy] you wouldn't actually be able to tell if this is where the bottleneck is and that's why the horse is not processing as much energy."

Jones added that while performing a muscle biopsy is valuable in detecting structural abnormalities or pathologies, much more research needs to be done into how equine muscles function before clinicians will be able to tell trainers precisely how to alter their training programs to achieve optimum performance in a particular horse.

Denise Steffanus is a contributing editor of Thoroughbred Times who writes frequently on veterinary and farm management topics.