On Matters ... Equine

By Dr. Jim and Lynda McCall

In the deep South, the summer daylight hours can be so oppressive that most horse events begin about five p.m. Several summers ago, we hosted a nighttime cutting where they started to settle the cattle about dusk. An acquaintance of ours, riding a cowy little mare, came to help. He rode the mare through each bunch of calves; he turned back for the cutters, he held herd; he even showed the mare in a class or two. By three a.m., the mare was spent — sweat pouring off her body, muscles trembling. Her rider pulled his tack and led her over by the barn to hose her off with plans to walk her dry. Unfortunately, it was much too late for this to be a viable plan.

As the cool water hit the mare’s body, her muscles began to stiffen. By the time the washing was complete, the mare was locked down tight and rigid as a board. We happened by as a group of concerned horsemen were discussing the next course of action. They had decided to force the mare to move — thinking she would gradually work out of it.

WRONG! Recognizing that this mare had exertional myopathy (in other words, she had tied-up), we quickly tried to intercede on her behalf. Forcing the mare to move would have caused muscle damage that could take months to heal. Shocked to learn of this, her owner decided to follow a different course of action. The mare was allowed to remain where she stood. With all the commotion of the other horses and horse trailers pulling out, a tranquilizer was given to encourage a quiet attitude.

Fortunately, it was only about five steps to a stall and, within two hours, the mare showed signs of limited mobility. She was then moved into the stall and plans were made for her owner to return at the end of the day to haul her home. Twelve hours later, the mare was still a little stiff but no longer appeared to be distressed. She loaded easily into the trailer and her owner reported that she was back to her old self in about two weeks.

This is the kind of muscle malfunction that is most often associated with racing or timed event competitions. Symptoms include profuse sweating, trembling, rapid pulse, weak hind limbs and a stiff gait accompanied by a reluctance to move. Even though physical exhaustion is usually the trigger which sets a horse up for this condition, it is generally believed that the cause is rooted in the diet — the focus centering on total energy intake.

Another expression of this condition, Monday Morning Disease (or azoturia), may be helpful in understanding this relationship. The story with horses suffering this plight, oftentimes, goes like this: A horse is fed large amounts of high energy feed, which provides him with the nutrition to daily perform high-energy exercise. Then the animal is given a day off but the feed amount is not reduced. When the horse is again asked for his high energy performance, his muscles respond by tying-up.

This common explanation is an oversimplification of this classic syndrome. Horses can tie-up after any strenuous physical exercise, even when they have not been laid off. And not all horses seem to have an equal chance of being at risk. Mares are more likely to tie-up after strenuous exercise than colts — especially mares in heat. Could it be that the high levels of estrogen (the female hormone associated with the onset of estrus) predispose some performance mares to tie-up?

Scientists are unsure, but they do believe that the source of the problem involves body chemistry imbalances. This assumption naturally leads us to look to nutritional management for solutions.

The first thing to do to decrease the chance of your performance horse tying up is to reduce its feed consumption during days off. Then particular attention should be given to the minerals available to the animal. Horses being conditioned for peak performance need larger amounts of specific minerals than the average horse.

The following are the latest National Research Council recommendations for these important minerals in horses under an intense exercise schedule:

Calcium, 43.9 grams per day; phosphorus, 29.9 grams per day; magnesium, 15.1 grams per day; potassium, 49.8 grams per day; sulfur, 17.2 grams per day; salt, 60 grams per day. Many times these needs can be met simply by providing the horse access to an electrolyte supplement specifically designed to supply higher levels of these minerals.

Both of these first two suggestions are aimed at preventing exertional myopathy. Avoidance of this condition is much easier than trying to uncover a cure. Tying-up can be caused by a variety of imbalances, therefore there is not just one remedy. And once a horse has had the misfortune to tie-up, he appears to be more vulnerable to the condition.

For horses that seem to habitually want to tie-up, injections of various vitamin and mineral compounds may provide some relief. Two commonly used products are ESE and thiamine. ESE is an injectable form of Vitamin E and the mineral, selenium, two additional nutrients with an increased requirement in horses under heavy exercise. These chemicals working together as antioxidants spare vitamin A. Thiamine, alias vitamin B1, is also available as an injectable and routinely used in the treatment of tying-up. Since thiamine is an intregal part of energy metabolism, it is suspected to be deficient in horses involved in heavy exercise programs. (Brewer’s yeast is also an excellent source of Vitamin B1.)

So what does all this mean to the average horseman trying to get this horse ready for competition? As the level of fitness increases, diet becomes more important. To be able to compete successfully in high-energy, fatigue-producing events, care must be taken to provide the horse with all the additional nutrients such exercise demands. If you need assistance in developing a feeding program that will provide this higher level of nutrition, there are several resources which may be available to you. Call your county Extension office to see if your state has a horse Extension specialist. Chances are he will either be able to work with you or will direct you to an equine specialist in your area. And don’t overlook your local veterinarian. A little research on your part will go a long way. While we don’t know a lot about why some horses tie-up, one thing is apparent. Tying-up occurs less frequently in the horses of owners and trainers who pay attention to the details of proper nutrition.