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Equine obesity


If there is any truth to the idea that after a while owners start to look like their pets, then many horsemen and women need to go on a diet.

If there is any truth to the idea that after a while owners start to look like their pets, then many horsemen and women need to go on a diet.

The general equine population of the United States is working less, eating more and becoming fat.

Advances in nutrition and in pasture management over the years have led to better-fed horses and clients have been educated about equine dental care, appropriate deworming programs and other aspects of good husbandry that make it easier for horses to get fat and stay that way.

Horses need exercise, but that can vary from structured, intense exercise such as these horses about to begin a 50-mile endurance ride, to an easy trail ride or simple daily walk.

Education needed

This does not mean that we are treating horses too well, only that more education needs to be done.

Veterinarians should make clients aware of the problems associated with obesity in horses and encourage them to make a distinction between fat and fit.

This topic is especially important as summer approaches bringing with it lush, green, "carbohydrate-loaded" grass and the potential for overweight horses to, nutritionally, go overboard.

Obesity disease link

Many new studies are linking obesity to a variety of disease conditions in horses.

Dr. Philip Johnson, professor of equine internal medicine at the University of Missouri College of Veterinary Medicine, has been investigating the links between obesity and laminitis.

Johnson is especially interested in the possible association between laminitis and the medical condition known as glucose intolerance or insulin resistance. This condition is similar to the early stages of what, in humans, will become Type II or adult onset diabetes.

In this "politically correct" era, whether you call them "vertically challenged" or "full-figured", a fat horse is not difficult to identify. This horse shows the typical cresty neck, lack of rib or body definition and deep back and rump furrows seen in the overweight horse. One of the most difficult aspects of dealing with these horses is convincing owners that overfeeding is not healthy. Many owners equate equine food with care and concern and feel that a fat horse is a happy one.

Many veterinary researchers now feel that a similar condition exists in horses and that obesity is strongly related.

"Obese horses and ponies with laminitis are also commonly affected with insulin resistance," noted Johnson, and current studies are attempting to determine which condition comes first. Do horses become obese because of insulin resistance and do vascular changes due to obesity then cause laminitis? Or can the increased levels of insulin (hyperinsulinemia) seen as the horse's body responds to insulin resistance cause or potentiate obesity and also be a primary factor in the development of laminitis? These are very active areas of current study and the preliminary information is leading to many more questions than answers so far.


Drs. Donaldson, Jorgenson and Beech from the New Bolton Center at the University of Pennsylvania School of Veterinary Medicine, recently looked at a number of horses that had laminitis. They were looking at the association of impaired pituitary function in horses with laminitis, but they also noted that a number of horses in their study had no pituitary dysfunction but did have hyperinsulinemia.

"Because most of these horses were overweight," say Donaldson, Jorgenson and Beech, "it is possible that hyperinsulinemia was associated with obesity."

These researchers then went on to state that "alterations in glucose metabolism (such as insulin resistance) have been implicated in the pathogenesis of laminitis."

They noted that obese humans with insulin resistance have abnormal activity of 11 B-hydroxysteroid dehydrogenase-1 (11B-hsd1) which is an enzyme that activates cortisol. This enzyme is also believed to be abnormal in horses with laminitis.

One horse in their study had a high insulin concentration, hyperglycemia, a cresty neck and a body score of 8/9. This horse was treated with dietary restriction, phenylbutazone and corrective trimming.

After four months of consistent treatment/management, the horse's body weight had decreased by 14 percent, insulin and glucose concentrations were within normal range, body score was 5/9 and the horse was now sound.

While this is just one example, it does suggest the possibility that obesity itself is a potential cause or factor in some of the most difficult diseases of horses and that treating obesity may be as important as any other treatments that veterinarians can offer.

Efficiency loss

Laminitis and insulin resistance are not the only conditions that are being linked to obesity.

Overweight horses are less efficient athletes.

This may sound immediately obvious but is not being appreciated by some owners and trainers. Some horsemen and women like to see fully rounded horses in the show ring. This would be good if that appearance was due to fit muscle, but too often overfeeding is replacing adequate conditioning.

These heavy horses show decreased exercise tolerance and increased stress on joints and soft tissue support structures, which often leads to more injuries. Arthritis can be accelerated by increased body mass as well.

Increased oxygen need

Overweight horses have increased body tissue and alterations in blood flow. This leads to an increase in the amount of oxygen needed, especially during exercise.

Yet these animals have a harder time taking in oxygen because this increased body mass restricts chest wall motion. This increased fat layer also makes thermoregulation more difficult and fat horses are more prone to problems during the hot summer months, which is the peak time for most equine competitions.

Increased heart rate (due to blood flow restrictions) and increased respiratory rate (due to increased oxygen need and attempts at heat dissipation) can cause increased levels of blood lactate which can lead to tying up or exertional myopathy.

Additionally, increased fat storage in the liver can decrease this organ's function. Increased fat content in the body is believed to increase the risk of fatty tumors, particularly lipomas, that can grow in the omentum of the abdomen, strangulate intestine and cause colic.

Obesity decreases immune system function and can make horses less resistant to some diseases.

Problem pregnancies

Overweight mares can have difficulty reproductively and high fat scores have been associated with increased duration of pregnancy, increased placental weight and decreased milk production as well as difficulty in rebreeding.


Recent research has shown that horses consuming a high-energy diet show exaggerated post-feeding insulin levels and that the body's response to this dietary challenge can contribute to or cause osteochondritis dissecans or OCD.

This research reported that 100 percent of foals consuming a diet that provided 129 percent of NRC dietary energy recommendations developed OCD lesions, while only 17 percent of foals consuming 100 percent of NRC dietary energy recommendations developed similar lesions.

These researchers pointed out that modern day equine diets contain high-energy cereal grains that are high in starches and that such diets are known to increase both blood glucose and insulin levels following consumption.

It is being proposed that such diets are increasing OCD by altering insulin mechanisms in horses.

View from Down Under

Dr. Nerida Richards, a nutritional consultant Ph.D. based in Australia, has a different idea on this new research, however.

She notes that in this new research, horses on the farms with the highest incidence of OCD were 15 percent heavier than the average of 350 Kentucky weanlings. Weanlings on a farm with a 0 percent incidence of OCD were 3 percent lighter than the average of 350 Kentucky weanlings.

She postulates, "the elevated insulin responses observed in horses with OCD may be merely a symptom of their excessive body weight and fatness and not a cause of OCD as has been suggested."

Pretty simple, afterall

All of this information seems to be telling us what we have intuitively known all along.

It is not healthy for horses (or any species) to be overweight, and that treating obesity may, in fact, be much more important than previously thought.

Treating obesity in horses, however, is probably harder than was previously thought because the answer is diet and exercise and this becomes a management and compliance problem.

The only way to reduce obesity in horses is to decrease dietary energy intake and to increase exercise.

Often, exercise is difficult for overweight horses so it is best to start slowly. Walking can be a simple first step followed by easy trail riding and progressing to more strenuous activity, as the horse will tolerate it.

This exercise must be done on a consistent basis and it cannot be stressed strongly enough to clients that it must be done. Simple turnout on a "dry lot" or depleted pasture is helpful, but not enough. Exercise must be part of the equation to increase metabolism and to help use stored fat supplies.

Reduce pasture exposure

Pasture grass contains a large amount of energy and horses at pasture graze around 70 percent of the time. This exposure must be reduced.

Horses are designed to graze and eat continuously, however, so there are limits to the reduction that you can make.

The standard guideline is for a horse to receive at least 1 percent of ideal body weight in grass per day. This equals three flakes of hay or comparable grass amount per day.

Many horses will be bored on this small amount of hay or grass, and the development of pasture or stall vices such as cribbing or chewing can be a complication when trying to restrict a horse's intake.

Experts recommend making the horse work harder and longer for its food. Spread the hay out in multiple locations in the pasture or stall, use a grazing muzzle to slow the horse's intake, place the horse in a larger field or pasture and make it move to get to water and feed. All of these are small points but may help in reaching the desired goal.

Grain feed

Reducing grain feed is at the core of most equine diets.

Many horse owners complain that their horses already consume "just a small handful." These horses are not receiving enough vitamins and minerals to satisfy their requirements and are at even more risk for problems.

Most horses should consume a diet that reduces energy while maintaining vitamin and mineral balance.

Newly available "lite" feeds provide this option.

"Most feeds are designed to provide balanced vitamins and minerals if fed at about 5 lbs./1,000 lbs. of body weight," says Dr. Marty Adams, Ph.D., of Southern States, a major feed company. "Our 'Triple Crown Lite' feed," continues Adams, "has a higher rate of vitamins and minerals so that the owner can drop the volume to 2 lbs./1,000 lbs. body weight and still provide adequate vitamin and mineral content, which is crucial if that owner is also restricting pasture exposure as part of a diet plan."

Many new reduced-energy feeds from other quality companies are coming on the market with similar approaches to weight reduction for the fat horse. These feeds are designed to allow the horse to eat enough grain to keep it behaviorally content while avoiding excess calories and still ensuring adequate vitamin and mineral intake.

As Dr. Bill Vandergrift, a Ph.D. nutritional consultant, writes, "The operative word in putting horses on diets is moderation. Take your time. Forcing your horse to lose weight too fast will make him hard to live with and can create metabolic problems."

Design a program and stick with it. Weight loss may take six months or more but it will occur if the approach is sound and the commitment is strong.

This is where veterinarians can do the most good and where education becomes important.

It would be nice to offer a new drug or procedure to treat obesity quickly and easily and most clients would prefer that as well (as evidenced by the approach to human weight loss by many people), but diet and exercise are still the best approach and must be stressed.

It is becoming clear that obesity is a developing problem in the equine population and that this disease can contribute to or cause a number of serious problems for horses. No one likes to diet and this goes for horses, too.

Veterinarians should provide the needed nutritional consulting, make dietary recommendations and design and support an exercise program.

Teach clients to evaluate their horse's body condition, monitor glucose and insulin levels when necessary and reassure clients that, in the long run, a thinner horse will be a happier, healthier one.

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