Equine Weight Management: Facts and Fiction

Equine Weight Management: Facts and Fiction

For most overweight horses and ponies, try strict diet and exercise to help them shed pounds before turning to pharmaceutical or supplemental options.

Photo: iStock

In general, weight gain or loss is a matter of energetics and the first law of thermodynamics: Energy can neither be created nor destroyed, just converted from one form to another. Thus, energy within adipose tissue cannot be destroyed but must be converted to another form, such as energy used to contract the muscle during exercise. Therefore, within reason, weight gain or loss is simply a matter of caloric calculations. Every horse (or human) is different, and individual metabolism may not be accurately estimated, thereby confounding our calculations. Despite this fact, several companies claim to have products that magically add weight or reduce body fat.

Weight-Gain Products

There are numerous products out there to help horses gain weight. A careful examination of the contents likely reveals that one of the top ingredients is going to be some kind of high-fat ingredient (such as vegetable oil). If the overall calories in these products are estimated, it is probable they will be higher than the amount of calories in regular grain mixes, but less than those found in straight vegetable oil. Therefore, it may be cheaper and easier to feed your horse vegetable oil. However, if your horse is finicky and doesn’t like straight vegetable oil, these products may be very worthwhile. In addition, many of these products use fat sources such as flaxseeds, so you may see a shinier coat as well. Thus, weight gain products can work to help your horse gain weight.

Some horse owners believe that if a horse is to gain weight, particularly muscle, they should increase the protein in the diet. However protein is not a very efficient energy source, and energy is what is required to create and store fat. Also, protein alone will not build muscle; work is required to do that. When a horse is put into work, its protein requirements will increase to help support muscle development, but this is usually easily met through increased feed intake to support the exercise itself. Therefore, just adding protein to a horse’s diet will not help him gain weight.

Weight-Loss Products

There are no simple solutions to losing weight (if there were, we wouldn’t see such an obesity problem in our human population either); however, many products are marketed to help a horse lose weight and/or improve insulin sensitivity. One product commonly given to horses is thyroid hormone medication. The thyroid is a gland that produces hormones (thyroid hormones) that help regulate overall metabolism. If the thyroid gland is underactive (hypothyroid), it will not produce as many thyroid hormones in the system, thereby slowing the body’s overall metabolic rate and predisposing an individual to gain weight.

It was once believed that all overweight horses were hypothyroid. However, this was usually untrue as the tests to measure thyroid hormone status in horses at the time simply weren’t very accurate. These horses were often prescribed thyroid hormone medication to increase their metabolic rate and assist with weight loss. Thyroid hormone treatment can in fact help horses lose weight.

One study examined the use of thyroid hormone medication in healthy normo-thyroid horses (horses with normal amounts of thyroid hormone being produced naturally) and found that these horses lost weight and had significantly increased insulin sensitivity following treatment (Frank et al., 2008b). Thus, there may be some benefit to such use of thyroid medications for extremely obese horses. It should be noted, however, that in humans, thyroid medication (especially when given to those who are not hypothyroid) is associated with cardiovascular complications and, therefore, not prescribed except in cases of hypothyroidism. The aforementioned equine study did not detect any cardiovascular issues (Frank et al, 2008a), but cardiovascular problems may still be a concern. With an extremely obese horse, the risk of laminitis may be greater than the risk of heart problems, and thyroid hormone medication may be useful. For most horses however, strict diet and exercise should be attempted first.

Several other human drugs are used to treat insulin resistance. Two studies have examined the effectiveness of one such drug, Metformin, on insulin sensitivity in horses, with conflicting results (Durham et al., 2008, Vick et al., 2006). Metformin appears to have low bioavailability in horses, compared to humans, which may explain why it hasn’t proven to be effective in horses (Hustace et al., 2009). Additional work is required to examine the effectiveness of other potential drugs on horses.

Many other non-drug supplements are available to horses and believed to affect insulin sensitivity. However, because these products are not considered drugs, they are poorly regulated. There are a few key ingredients that may have some benefit to insulin sensitivity, although evidence in horses is lacking. Magnesium and chromium, as well as general antioxidants (such as vitamin C and E), are believed to have some function counteracting insulin resistance and possibly affect body weight. However, adequate clinical evidence is lacking in humans and no research in horses has reported any benefits (Guerrero-Romero and Rodriguez-Moran, 2005).

Nonetheless, these nutrients (namely chromium and magnesium) likely won't hurt the horse when fed in amounts according to instructions, so if economically feasible there is no reason not to try them. That said, they should not serve as a replacement for exercise and caloric intake restriction. Cinnamon and other herbal compounds are often fed to horses in hopes of improving insulin sensitivity. However, as reviewed by Tinworth et al. (2009), many herbal products do not have scientific research to support their claims, and many have not even been studied for safety in horses.

Some horse owners believe that weight can be gained or lost in specific physical locations, depending on diet. For example, some owners would prefer that fat be deposited along the buttock region to make the hindquarters appear larger and more developed, with fat being reduced along the crest of the neck. Similarly, some owners aim to “work” certain regions of the horse’s body in attempt to reduce fat in that area. Unfortunately, there is no way to “spot reduce” in horses or humans; fat is lost approximately in equal amounts from all parts of the body, regardless of the exercise.

However, genetics does play a role in determining what areas are more prone to store fat. This is highlighted in people where some carry their weight around the midsection and some carry excess weight in the hips and thighs (the apple vs. pear shape). It is possible that horses also have genetic predispositions to be either “crestier”—and carry fat around the crest of their neck—or to be more prone to developing a ridge down their back with excess fat coverage. It is unknown if there are greater health concerns associated with where a particular horse carries his fat, as there are in humans.

Another common misbelief among horse owners is that the hay belly results from a horse being too fat. The hay belly, or enlarged gut region in some horses, is mainly due to the fact that within this region lies the fermentative area of the large intestines. If a horse is offered relatively low nutritional quality feed, it is believed that the intestines will retain the feed longer in effort to ferment it to a greater extent and to extract all possible nutrients. Thus, if the fermentative vat is more active, it stands to reason that the gut area would increase. One way to help counteract a hay belly is to decrease the required fermentation time by improving the quality of the forages. This may not be recommended, however, for overweight horses.

It should also be noted that some horses simply have a larger gut region, and altering the diet won’t affect it. To avoid being misguided about weight gain or loss, horse owners are encouraged to educate themselves and research various compounds and products. Before purchasing a product, ask companies for publications of their study results proving the product’s effectiveness.

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