Weight Gain in Skinny Horses: Four Tips

Achieving weight gain in skinny horses is often a matter of reworking the diet to maximize energy consumption. Commonsense approaches to weight gain involve bumping up forage quality and quantity, adding a suitable concentrate, or supplementing with a high-calorie additive.

Forage quality. Many horses are able to gain weight with daylong grazing on high-quality pasture. This is especially true in the spring when a flush of fresh grass is available. Not all horses can handle full-out access to pasture, so consult a veterinarian if a horse has a history of metabolic disease or laminitis.

“Do not, however, let grazing recommendations intended for horses with specific medical conditions undermine sound practices for healthy horses. For most horses, grazing is the most natural way to provide nourishment,” said Catherine Whitehouse, M.S., a nutrition advisor at Kentucky Equine Research. “If healthy horses gain weight rapidly on pasture, then appropriate measures can be implemented to reduce intake and slow or halt weight gain, such as the strategic use of grazing muzzles, drylots, and limited grazing times.”

If a healthy horse is on pasture in late winter and remains on pasture as the spring green-up occurs, there is likely little need to worry about acclimating him to grazing. If a horse is being introduced to spring pasture without the benefit of grazing during green-up, it is best to do so in short bouts, with the first session an hour or two long and then increasing by an hour or two daily. Gradual increases in grass consumption will help the microbes of the hindgut become accustomed to the new forage.

In terms of hay, consider best-quality grass or legume hay for horses in need of weight. Top-drawer hay will cost more than mid-quality because of its rich energy content. “Avoid any hay that is discolored (yellowish-green might be fine; icky-brown is not), musty, dusty, or moldy. Keep an eye on how well the skinny horse cleans up its hay, as horses must eat to gain weight, and anything off-putting to the horse will thwart weight gain,” recommended Whitehouse.

Aside from good-quality pasture and hay, alternative forage sources often have a place in the diets of skinny horses, primarily because they are consistent in quality and palatable to most horses. Alternative forages include hay cubes, hay pellets, and certain fermented forages. These are somewhat underused sources of calories, Whitehouse said, but they are useful in many circumstances, especially when high-quality forage is difficult to obtain.

Forage quantity. Horses require substantial fuel for growth, performance, and reproduction, as well as to power everyday body processes. As grazing animals, forages are the primary energy sources for healthy horses.

A healthy horse with a normal metabolic rate that requires neither weight gain nor weight loss would likely maintain condition on 1.5-2.2% of its body weight in forage per day. For a 1,250-lb (570-kg) horse, this would equate to 19-28 lb (9-13 kg) of forage daily.

Horses that require weight gain can be offered more forage than this, up to 3% of body weight. Maximal forage intake is 3-3.5% of body weight per day for most horses, though lactating mares and other horses with extreme energy needs might consume 5% of body weight daily.

When feeding hay or alternative forage sources, astute management can help determine how much forage should be fed. When feeding for weight gain, some horse owners will offer free-choice forage, adjusting the amount based on whether the horse cleans up what is offered or leaves a portion.

Also keep in mind horses on all-forage diets require vitamin and mineral supplementation for optimal health.

Concentrates. Most horsemen think of concentrates as energy-dense textured or pelleted mixes of cereal grains, protein sources, and molasses. Fortified concentrates are enriched with protein, vitamins, and minerals, with the level of fortification dependent on the class of horse for which the feed is intended. Concentrates are appropriate for weight gain, though careful selection of concentrates might be necessary for some health issues.

For mature horses in need of weight gain, it is often wise to choose a concentrate that contains a variety of energy sources, meaning the feed includes starch (corn, oats, barley), fat (vegetable oil, rice bran), and fermentable fiber (soy hulls, beet pulp, alfalfa meal). Feeds intended for performance horses often feature these blends, as do feeds manufactured for senior horses.

“Typically, fortified concentrates are formulated to be fed at a level of intake between 5-13 lb (2.2-6 kg) per day. A common mistake made with concentrates is to feed less than the minimum recommended level, a practice that could lead to suboptimal vitamin and mineral nutrition,” said Whitehouse. “In the case of the skinny horse, underfeeding would preclude or slow weight gain. Therefore, be sure to follow the manufacturer’s recommendation in figuring how much to feed.”

While feeding one or two meals per day is the standard practice for many horse owners and managers, skinny horses sometimes do well when fed the total amount of concentrate split among three or four meals per day. Some horses simply process small meals more efficiently than large meals, Whitehouse explained.

High-Calorie Supplements. Energy-dense supplements can be added to the diet to increase calorie consumption.

In the past, one of the most popular supplements was corn oil. Research has indicated that corn oil, because of its high omega-6 content, is not the best choice. “Other vegetable oils offer the same caloric benefit but with higher levels of beneficial omega-3s; these oils include canola and soybean oils,” explained Whitehouse.

Fish oil provides the highest quantity of omega-3s, and the numerous health benefits associated with them, but it is generally not used as a source of supplemental calories.

Horses have different palates when it comes to oil. If introduced gradually over a period of one to two weeks, most horses will accept vegetable oil added to their concentrates. Amount of oil fed will vary depending on the caloric needs of the horse, but many owners work up to a total daily amount of between one and two cups (250-500 ml; 8-16 oz), split between meals.

Another common high-fat supplement beneficial for skinny horses is stabilized rice bran. Highly digestible and palatable, rice bran contains about 20% fat. Like vegetable oil, it is usually top-dressed onto concentrate meals. Typical serving size for rice bran is 1-2 lb (0.45-0.9 kg) per day, divided among feedings, though more can be fed if necessary. Review the manufacturer’s instructions prior to feeding.

Developing and then fine-tuning a diet for an underweight horse requires an understanding of how  best to deliver energy. Advice from nutrition advisors at Kentucky Equine Research is available. Start by completing this questionnaire.