We hear so much these days about overweight horses and their health problems, that those of us with underweight patients feel almost fortunate! But don’t be too complacent. Any time a horse can’t maintain a healthy weight, there’s reason for concern.

Horses vary in their ability to burn calories. Their “metabolic rate” is influenced by genetics and body composition. We all know Thoroughbreds have a genetic tendency to be on the lean side, and a highly muscular horse will have a faster metabolic rate than one who is out of shape.

But what about the true “hard keeper” who cannot seem to gain weight? Throwing more feed at him is not always the correct approach. You have to rule out a few things first, to make sure there isn’t an underlying problem.

Four causes of weight loss

1. Dental problems — The most common reason for weight loss is poor teeth. A horse’s teeth should be floated at least once each year, but some horses need their teeth floated every six months. Poor dental maintenance can make eating a painful experience.

Older horses sometimes lose teeth, making hay chewing virtually impossible. These horses need to have softer feed, but still require a forage-based diet. Soaked hay cubes offer a good solution.

If you come across a horse who is dropping his feed or spitting out clumps of partially-chewed hay, the situation may require the services of an equine dentist.

2. Parasites — Another common reason for a horse to be underweight is inadequate internal parasite control. Worm infestations can vary by region, but don’t assume that if a horse stays in one paddock or barn all the time, he doesn’t need an effective parasite control program. Worms can damage the intestinal lining and the blood vessels that support the digestive system, diminishing nutrient absorption and, in actuality, starving the horse.

3. Flora imbalance — A horse’s hind gut contains billions of beneficial bacteria that produce enzymes for digesting forage. Without these bacteria, the horse could not derive any calories from hay and pasture. So keeping these bacteria healthy is a must. Their numbers can diminish due to illness, stress, over-consumption of cereal grains, and antibiotic therapy (which kills beneficial as well as harmful bacteria). Colic can result if their numbers diminish too much.

In the generally healthy underweight horse, the level of helpful microbes can be slightly off. A prebiotic is therefore a useful addition to the diet. A prebiotic is different than a probiotic because it does not contain any live microbes. Instead, it contains bacterial fermentation products that feed the existing bacterial flora in the hind gut, making them healthier and better able to digest forage. The result is weight gain, since the horse can get more calories from the fiber found in hay and pasture. Ration Plus is an excellent prebiotic. A probiotic (live microbes) is useful for a horse on antibiotic therapy, to replace the beneficial bacteria that have been destroyed.

4. Vitamin deficiencies — Borderline B-vitamin deficiencies can lead to a poor appetite. There are eight B vitamins that rely on each other to keep a variety of body systems in good working order. The digestive system relies on B vitamins to keep healthy. In addition, each cell in the body requires several B vitamins to metabolize nutrients for energy. This means a horse owner can feed an excellent diet, but if there aren’t enough B vitamins in the bloodstream, the horse’s tissues will not be able to derive calories from the carbohydrates, fats, and proteins in that diet. The result is weight loss due to malnutrition at the cellular level. Recommend a B-complex preparation such as BPlex (Horsetech) that provides only B vitamins. Avoid “blood builders” that have B vitamins with added iron. There is plenty of iron in hay and pasture, and too much can be harmful.

Adding calories

Once you’ve ruled out any medical problems or B-vitamin deficiencies, you can work on providing more calories. Your best approach is to get the horse owner to add concentrated calories, so she doesn’t have to feed too large a meal. Horses’ stomachs are relatively small, compared to the rest of the digestive tract. So, for the average 1,100-pound horse, meal sizes should be limited to no more than 4 pounds. Advise the owner to get a scale and weigh the feed – she shouldn’t rely on a scoop or coffee can as they tell you nothing about weight, only volume.

Carbohydrates from cereal grains (oats, corn, barley) provide less than half the number of calories than fat. So the best and easiest way to add more calories without more bulk is to add fat to the diet. Flaxseed meal is excellent. Not only is it high in fat, but it’s high in beneficial Omega 3 fatty acids that reduce inflammation, protect joints and hooves, keep the immune system healthy, and make the horse shine. Recommend a product that is stabilized and has added calcium to correct the naturally inverted calcium-to-phosphorus ratio found in flax. Do not suggest whole flaxseeds or those that are soaked — soaking destroys the Omega 3 fatty acids.

Another good fat source is rice bran. Again, recommend a product that has added calcium since you don’t want the horse owner to feed more phosphorus than calcium. Natural Glo (ADM Alliance) is an excellent rice bran product. And advise the horse owner to be consistent. Many riders like to give a warm bran mash once a week as a treat. This is asking for an episode of colic since the bacteria in the hind gut have to adjust to a new feed. So a new feed should be added slowly — over a two-week period — and fed daily.

Avoid adding soybean oil, wheat germ oil, or corn oil to the diet since they are high in Omega 6 fatty acids, which increase inflammation. If a horse has aging joints, these oils can increase his pain. Rice bran or canola oils are safe to feed since they are low in Omega 6 fatty acids. If a horse owner decides to add oil to a meal, recommend that she start with only one tablespoon per meal. She can slowly build up to half a cup per meal. Many horses do not like oily feed, so owners need to take their time. It also takes a few weeks for a horse’s system to adjust to extra fat, so patience is required.

The importance of forage

Finally, horse owners should feed their horses the way they are meant to be fed by allowing them to graze at all times. They can give their horses all the hay they want as long as it is nutritious, free from mold, and not filled with stems. The horse’s stomach, unlike our own, produces acid all the time. Chewing produces saliva, a natural antacid, to neutralize stomach acid. If forced to go for hours without anything to graze on, a horse will suffer physical stress (because he is in pain), will often develop bad chewing habits, may colic, and will have difficulty gaining weight.

If possible, suggest that the horse owner add about 20% alfalfa hay to the mix. Alfalfa is a legume and will boost the overall protein quality in the diet, making body tissue production more efficient. Alfalfa is also higher in calories than most grass hays. Overall, alfalfa benefits a horse’s health through additional quality protein, added minerals, and more calories. So it’s okay to allow horses to enjoy this nutritious hay.

Always rule out potential health issues before simply increasing a horse’s caloric intake. Giving more feed to a horse without discovering the root of the issue simply wastes time and money. Remember to adjust a horse’s diet slowly and consistently. By following these guidelines, you can help turn a hard keeper into a picture of equine health!