Are specialty diets practical?

Humans have been feeding horses for centuries, so you would think that we'd have it just about figured out by now. Yet new research seems to come out every year. We currently know more about the nutritional needs and requirements of horses than we have ever known. The recent American Association of Equine Practitioners (AAEP) convention held in Denver in December marked yet another step forward in both knowledge and confusion relating to equine nutrition. Knowledge stems from the scientific community providing diets that can aid in the treatment of many equine diseases, and confusion persists because these varying diets will make feeding decisions and feeding practices much more difficult for horse owners and trainers.

This horse shows a cresty neck and fat deposits behind the elbow and along the hips and rump. It could be insulin resistant/glucose intolerant, pre-laminitic Cushingoid, or simply fed too much for its work level. A horse with any of these possible conditions will benefit from a feed that has a low sugar/low starch base along with other components that can help the body respond to these potential problems. (Photo: Ken Marcella)

Most of the major feed companies were in attendance at the trade show at the AAEP convention, and almost all were giving out new educational materials to veterinarians. A slow progressive trend toward specialty feeds during the past few years finally has become a fully developed concept, and now there are a large number of specific feeds, each targeted at a specific equine disease or condition. At first, the needs of young, growing, working, sedentary and older horses were separated, and veterinarians and owners were introduced to feeding for different life stages. Now there are feeds for many disease conditions, and owners have many more choices to make. This adds to the uneasiness felt by horse owners when it comes to choosing feeds for their animals.

A recent survey conducted by Triple Crown Nutrition shows that veterinarians are the most recognized source of feeding information for horse owners. It will be the equine veterinarian's job to introduce clients to this new feeding concept and to help them deal with the confusion that all these new choices will create. Additionally, trainers with large barns full of horses will have to try to negotiate between the benefits of many specialty feeds and the realities of management limitations. The more horses receiving individual feeds, the more chances for confusion and mistakes because, in most commercial operations, the owners/trainers seldom are doing the actual feeding themselves. Will the thin horse in heavy work stalled next to the laminitis-prone overweight horse lead to a problem if individual feeds are swapped mistakenly? Again, clients most likely will look to their veterinarians for nutritional and management advice.

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Condition specific

Most feed companies are addressing the same diseases and types of equine disorders. These individual companies may vary slightly on the content of a feed targeted for a specific disease, but most of the feeding principles being used by all companies are the same. A look at the general concepts used to design feeds for specific conditions may help veterinarians understand these diets and their potential uses better.

Glucose intolerance/insulin resistance and problems with carbohydrate metabolism are being diagnosed with increasing frequency in horses. As veterinary knowledge and scientific understanding of these conditions increase, more horses may yet be included in this large category. The guiding principle for feeding these horses is to lower the amount of soluble carbohydrate and increase the fat and fiber. The feeds being produced for these horses try to control starch and sugar and often contain higher levels of certain vitamins and minerals that have been shown to increase and optimize metabolism, such as vitamin E, zinc, chromium and magnesium. The research into feeds for these conditions has been so aggressive that some low-sugar/low-starch feeds have been formulated to have less carbohydrate content than even a diet of simply hay. Horses diagnosed with equine Cushing's disease, glucose intolerance/insulin resistance or other types of carbohydrate metabolism problems, as well as horses suffering from laminitis, even if not affected with other underlying disease(s), can benefit from a these diets.

Veterinarians long have been treating horses with chronic obstructive pulmonary disease (COPD) with dietary management since "heaves" often can be influenced and affected by intake of dust, mold and any number of other allergens. Some of these allergy-inducing particles undoubtedly are taken in through the digestive tract. Because hay is a prime source of dust and mold in the diet of a horse, many of the feeds that have been produced to treat equine allergies are "complete" feeds that have a beet-pulp base as a highly digestible fiber supply. This addition to a horse's fiber intake allows owners to all but eliminate the feeding of hay or to use hay cubes, chopped forage or chaff products, which are much less prone to contain allergens.

Most practitioners and nutritional researchers agree that many cases of equine colic are related to nutritional mismanagement. Studies have shown that overloading the small intestine with carbohydrates reduces that section of the intestine's ability to correctly process feed, which leads to increased fermentation of starch in the cecum and colon. This tends to cause bacterial overgrowth, increased gas production and often leads to colic. Diets that are lower in soluble carbohydrates and that are highly digestible (pellets vs. whole grain) may be used with susceptible horses to reduce the risk of intestinal upset.

The clinical signs of equine polysaccharide storage myopathy (EPSM) or (PSSM) can be varied, and many horses exhibit these sometimes subtle gait alterations. Effected horses can show loss of muscle mass through the shoulders or hips. Abnormalities seen when flexing the stifle, such as shivers, stringhalt and patella fixation, all can be associated with cases of EPSM. Horses with this condition can show only excessive sweating with exercise or weakness and muscle trembling and difficulty when backing or turning. Some horses might be reluctant to have their feet picked up to be cleaned or trimmed and might stamp their feet or be reluctant to hold themselves on one leg for very long. It is thought that these horses suffer from a defect in glycogen synthesis regulation that makes them unable to metabolize starches and sugars properly. This defect results in levels of glycogen in the muscles of these horses that can be 1.5 times to 4 times higher than normal. The increased glycogen uptake in the muscle of these horses has been linked to an abnormally high insulin response. Though many facets of this response have been uncovered, there are more aspects that remain unknown. Nutritional treatment can be rewarding in some of these cases with the suggested diet attempting to reduce starches and sugars drastically. Fiber content is maximized for these horses and between 20 to 25 percent of the caloric requirements is provided by easily digestible fat. Higher fat requires increased vitamin and mineral levels, especially vitamin E, and most of the designed specialty diets reflect this need. These horses also should be restricted from access to lush pasture as exposure to fructan, a carbohydrate found in green grass following certain environmental conditions, can worsen EPSM. The use of dried forage substitutes or hay cubes can be beneficial in the management of these cases.

Weight control

While an increasing population of horses today suffer from obesity and need feeds that reduce carbohydrates, increase fiber, and balance vitamins and minerals, there are still a few horses that are "hard-keepers". These horses are generally those that lose weight during a strenuous show or competition season or horses that behaviorally do not show much desire to eat and gladly will leave the feed tub for turnout or other distractions. Feeding these horses can be a challenge, but there are specialty feeds to help. These high-energy diets generally are composed of high-fat and high-fiber ingredients with a source of highly digestible protein and increased amino acids needed for muscle development. These feeds also contain microbials, such as yeast cultures, enzymes and other metabolism enhancers, which help optimize digestion and aid in weight gain.

There are even more specialty feeds addressing other less-common medical conditions, such as tying-up (exertional rhabdomyolysis), hyperkalemic periodic paralysis (HYPP), behavioral conditions and so on. Yet these feeds still must be scooped out and put in individual feed pans every morning and evening, and this leads to a practical problem that is well understood by most commercial feed companies.

Jules Gagne, owner and trainer at Teamwork Dressage in Georgia, deals with the issue of feeding multiple horses daily.

"I simply cannot feed each horse a special diet in any practical way," she says. "So I stick to general principals with the majority of my horses and then give special feed to the ones that really need it."

This common-sense approach is echoed by Dr. Jim Ward, a veterinarian working for Cargill Feeds.

"The feed industry has put too much of a burden on management in the past, but we are trying to ease that burden," Ward says.

It is significant that almost all new diets start with a low-starch/low-sugar base because this addresses the vast majority of equine nutritional health issues. This principle makes it far easier to use one of these new feeds as a basic diet for most horses and then to tailor other feeds to fewer "problem" horses. This also reduces the chances of a serious incident resulting from a mix-up in feeding because — as Ward notes, and all trainers and barn managers know — "Murphy's Law is ready to strike at any time."

This practice of feeding a safe base feed that helps most horses will optimize the benefits from new diets and also will keep management practices simple. The fact that more specific and advantageous feeds are available for those horses that really need them will benefit veterinarians, owners and those specific horses, but the industry is not likely to continue further in this direction, Ward says.

"I do not see developing a 'Science Diet' approach to feeding horses because of the freshness and production issues," he says.

As a former owner and manager of a breeding farm, he also remembers the demands of that position and knows that such a feeding approach is all but impossible. The good news is that out of all the new research and new feeds has come a bit of simplicity, and this should make veterinary recommendations easier, owner decisions clearer and horse's nutritional management healthier.

Dr. Marcella, a 1983 graduate of Cornell University's veterinary college, was a professor of comparative medicine at the University of Virginia. His interests include muscle problems in sport horses, rehabilitation and other performance issues.