How To Help Your Underweight Horse


We hear so much these days about overweight horses and their health problems, that those of us with an underweight horse 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. This is referred to as their “metabolic rate” and 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 an underweight horse 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 an underweight horse

1. Dental problems – The most common reason for weight loss is poor teeth. Your horse’s teeth should be floated at least once each year, but some horses need their teeth filed down 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. So if you notice your horse is dropping his feed or spitting out clumps of partially-chewed hay, your first phone call should be to an equine dentist.

2. Parasites – Another common reason for a horse to be underweight is inadequate internal parasite control. Your veterinarian is your best source of information for this issue since worm infestations can vary by region. But don’t assume that if your 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 – Your horse’s hind gut contains billions of beneficial bacteria that produce enzymes for digesting forage. Without these bacteria, your underweight 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 feeds 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 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 you can feed an excellent diet, but if there aren’t enough B vitamins in the bloodstream, your horse’s tissues will not be able to derive calories from the carbohydrates, fats, and proteins in that diet. The result is an underweight horse due to malnutrition at the cellular level. Choose 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.

 Screen Shot 2014-04-01 at 2.05.55 PMAdding calories
Once you’ve ruled out any medical problems or B vitamin deficiencies, you can work on providing more calories to your underweight horse. Your best approach is to add concentrated calories, so you don’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 3½ pounds. Get a scale and weigh your feed – do not 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 your horse shine. Choose a product that is stabilized and has added calcium to correct the naturally inverted calcium-to-phosphorus ratio found in flax. Do not feed whole flaxseeds or those that are soaked – soaking destroys the Omega 3 fatty acids.

Another good fat source is rice bran. Again, choose a product that has added calcium since you don’t want to feed more phosphorus than calcium. Natural Glo (ADM Alliance) is an excellent rice bran product. And 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 add a new feed slowly – over a two-week period – and feed it 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 your underweight 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 you decide to add oil to meal, start with only one tablespoon per meal. You can slowly build up to half a cup per meal. Many horses do not like oily feed, so take your time. It also takes a few weeks for a horse’s system to adjust to extra fat, so be patient.

The importance of forage
Finally, feed your underweight horse the way he is meant to be fed by allowing him to graze at all times. Give him all the hay he wants but make sure your hay 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, 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 your horse’s health through additional quality protein, added minerals, and more calories. So allow your horse to enjoy this nutritious hay.

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


Dr. Juliet M. Getty holds a Master of Science and Ph.D. in Animal Nutrition. The winner of several teaching awards, Dr. Getty has taught comparative nutrition studies at the University of North Texas for 20 years. She consults privately with horse owners to customize feeding plans that address a variety of health conditions. Recently retired from academia, she now resides in Colorado, where she devotes herself full-time to equine nutrition. Her passion is to improve the lives of horses by helping their owners gain a better understanding of how and what to feed their equine friends. Dr. Getty has her own consulting company, Getty Equine Nutrition (GettyEquineNutrition.com) where she visits with horse owners, both locally and via phone consultations throughout the country and internationally. Watch for her new book (to be released this summer), an invaluable feeding reference for all life stages and conditions that horses experience.

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