Quarter Horses are popular horses for a variety of disciplines.

Post-exertion muscle soreness/strain can happen to any horse, but the high demands placed on the muscles of a Quarter Horse can easily lead to some soreness. Add to that the fact that they’re also prone to some breed-related muscle problems, and you know you need to pay attention to their muscles.

Slow, careful conditioning is the best preventative. Training improves both strength and flexibility of muscle groups and the tendons attached to them. Practicing movements in a controlled training setting will fine tune the reflexes the horse needs for quick changes of direction or fast starts. Training also improves levels of stored carbohydrate, glycogen, within the muscle, the only fuel that can support speed.

Feeding
There’s some evidence to support fat supplementation (up to 8%) of the grain portion of the diet in the hard-working Quarter Horse, despite our overall concerns about feeding fat to horses. Studies have found both improved sprint times and higher lactate production during sprints (an indicator of glycogen use) when grain was supplemented with fat.

The likely explanation for this is that the muscle learns to make better use of fat for maintenance energy requirements and during low level, slow work, allowing for better preservation of glycogen stores which are then available for the high speed work. It’s important to note, though, that this only works when fat is supplemented in addition to grain, not as a substitute for it as is done to treat Equine polysaccharide storage myopathy EPSSM. The horse still needs grain to build glycogen stores.

To benefit the most from training, and recover glycogen stores quickly after exercise, the muscle needs glucose. Studies in multiple breeds have shown that horses are slow to replenish their glycogen stores, taking up to three days to do so after a major effort. However, some recent studies have found that both intravenous and oral supplementation of simple carbohydrate can hasten this process. This trick has been practiced by human athletes for many years.

Details of how much, and when, for maximal benefit have yet to be worked out and confirmed by studies, but muscle in other species is most “hungry” for glucose in the first hour or two after exercise stops, with increased uptake by muscle continuing over the next 24 hours but dropping rapidly during that time. Providing the horse with 2 to 4 oz. of a glycogen-loading product such as those in our story on page 7, as a paste shortly after heavy training or competition, and again in a grain meal about two hours after the exertion, should give him a good head start on repair and replenishment of hard-working muscle.

Antioxidants are also important to hard-working muscles. They won’t boost performance per se, or prevent injuries, but they’re extremely important in mopping up the free radicals produced during exercise and preventing injury to cell structures.  Vitamin E and selenium should always be supplemented, according to the type of diet and selenium levels in your area.

Tying-Up
Isolated episodes of tying up can also happen to any horse and don’t necessarily indicate an underlying muscle disease. Severe overexertion may cause it, and electrolyte abnormalities may contribute to muscle cramping and pain. The precise cause of isolated episodes of tying-up often goes undiagnosed. 

Turnout is simply not adequate exercise to keep muscles conditioned and in shape.

Horses that are in the early stages of being introduced to serious speed work, and very fit horses that miss exercise sessions, are at highest risk. Cutting or even eliminating grain on days these horses are not formally worked can help decrease the risk, probably by avoiding excessive glycogen build up. Keeping horses outside, rather than stall confined, is also helpful.

Muscle is protein, and building/maintaining muscle requires protein. Most performance-horse diets contain more than enough protein to get the job done, but if the horse is failing to build or maintain muscle as expected, supplementation with HMB or a branched chain amino acid product may help (see story on page 7).

HYPP
Repeated episodes of tying-up symptoms of severe cramping are another story. HYPP and EPSSM are the most likely causes in a Quarter Horse. HYPP, hyperkalemic periodic paralysis, isn’t really tying-up, but it looks like it.

As most Quarter Horse owners know, HYPP is a genetically determined disease, tracing back to descendants of the great halter horse, Impressive. It’s really a disorder of electrolyte balance within the muscle, disturbing and reversing the normal condition of low sodium and high potassium inside the cell. In the early stages of an HYPP attack, muscles tremble and may spasm, leading to confusion with tying-up, but there are important differences (see chart).

Recommended management strategies include:

Avoid stress, changes in management, changes in diet.

Keep the horse on a regular exercise program.

24/7 turnout may be beneficial.

Avoid dietary high potassium.

Treatment with acetazolamide, a diuretic that encourages potassium excretion, for horses that are not well-controlled with management and diet.

Although some types of hay have been recommended as lower-potassium alternatives, the fact is that all hays are many times higher in potassium than the horse actually requires. Grass is, too, especially young growths of grass, but the high water content of grasses means the potassium is significantly diluted. Beet pulp without molasses is the lowest potassium feed, and grains are much lower than hays and will deliver a load of glucose at the same time, to help drive potassium into the cells where it belongs. Substituting wet beet pulp for part of the hay, frequent small grain feedings, and soaking hay before feeding, which will lower potassium content, are feeding strategies that help avoid swings in blood potassium.

In fact, the ability of insulin and glucose to drive potassium back inside the muscle cells where it belongs is the basis for owner’s first-aid emergency treatment of administering corn syrup, or encouraging the horse to eat grain (preferably corn). HYPP attacks are also a veterinary emergency, since the weakness can involve the muscles of breathing and severe attacks can kill a horse. Your vet will use intravenous glucose, possibly intravenous calcium and insulin, and acetazolamide.

EPSSM
Repeated episodes of true tying-up in a Quarter Horse, like in their heavily muscled cousins, the drafts, are most likely to be caused by EPSSM. Muscle biopsies of horses with EPSSM show high levels of glycogen as well as an abnormal substance that is not normal glycogen.

The exact nature of the defect in metabolism in these cells that makes them prone to damage with exercise isn’t clear, but it appears they rely too heavily on carbohydrate and not enough on fat. Limiting carbohydrate intake and feeding increased fat appears to “train” their muscles to make better use of fat as an energy source and relieve many of the symptoms.

Definitive diagnosis can only be made by muscle biopsy, although many opt for a trial of low-carbohydrate, high-fat diet rather than a biopsy. The current basic diet recommendation for an EPSSM horse consists of hay and substitution of the grain ratio with alfalfa pellets and up to two cups of vegetable oil. One cup of oil is the calorie equivalent of about 2.5 to 3 pounds of grain. Improvements in muscle tone (more relaxed) and frequency/severity of tying-up may appear rapidly or may take time.

Any oil will do, but Uckele’s Coco-Soya (www.uckele.com 800-248-0330, $12.30/gallon) can be a good choice. This blend of coconut and soy soil is cold pressed and unprocessed, retaining high levels of natural antioxidants. It’s highly palatable. The coconut oil is high in medium chain length triglycerides, which are able to enter the muscle cell without requiring a carrier protein like the longer chain triglycerides found in other vegetable oils do.

Treatment of an EPSSM-related tying-up episode is the same as for any other type of tying-up. Movement can worsen muscle damage and should be avoided. Muscle relaxants, tranquilizers and intravenous calcium and magnesium may be used to help the stiff, painful muscles relax. Intravenous fluids help prevent muscle pigments from clogging the kidneys.

Muscle Tears
Another problem that frequently occurs in Quarter Horses is muscle tears, due to the combination of heavy muscling and the type of work many Quarter Horses do. These typically involve long, large muscle groups of the upper hind leg, when viewed from behind.

Soreness and stiffness present at the time of the initial injury may resolve only to be followed by the development of a shortened gait on the involved side and a characteristic slapping down of the foot, called goosestepping. This occurs when the injured area of muscle heals by formation of a thick, tight scar that lacks the ability to stretch that normal muscle has.

The condition is called fibrotic myopathy. In some cases, calcification/calcium deposits may also form, called calcific myopathy. Surgical removal of the scarred and/or calcified portion of muscle is the usual treatment. Shock-wave therapy also has been tried.