The Thin Horse

Common causes of underweight horses

by R. Paul Schwab, DVM

One of the most common reasons for veterinary farm visits is to examine horses that are thin. This is especially true the last couple of years with the increase in animal welfare cases, abandoned horses, and the recession. Diagnosing reasons for weight loss can be challenging, especially if the horse’s history is unknown (e.g., how much they are eating, what shots they have had, etc.).

I find it easier to divide reasons for weight loss into four categories:

1. Nutrition

2. Teeth

3. Parasites

4. Everything Else

The first three are the most common reasons for weight loss and easier to diagnose and treat. The “everything else” category often needs the assistance of lab work, ultrasound, or trial and error.

Nutrition

Basically, horses need forage and a lot of it. A horse will consume approximately two percent of its body weight per day in dry matter, most of which should be forage (hay or pasture). This translates into about 20+ pounds of hay/grass for a 1000-pound horse. Weigh your hay periodically. Flakes of hay are not a good indicator of how much hay a horse is getting unless you know how much each flake weighs. Often, weight gain is as simple as feeding more food. Grain can be used to supplement the diet but should never be more than fifty percent of the ration unless it is a complete-type feed. Complete feeds have forage products added to them such as alfalfa, beet pulp, etc., that make them safer to feed at higher amounts. Other ingredients that are often used to help supplement forage include beet pulp, soy hulls, and fats such as rice bran and canola or corn oil.

Don’t forget about quality of feed. Forage can be extremely variable in quality depending on the time of year, type of grass, when it was cut, how it was stored, and other factors. Horses on poor quality hay might maintain their weight but probably won’t look very good and certainly won’t perform as well. If you purchase large amounts of hay at a time, or put up your own hay, consider using a forage testing service. The expense of the analysis is minor compared to the expense of treating sick or poorly faring horses.

Teeth

If your horse can’t chew properly, it can’t maintain weight. Dental problems can be as simple as sharp edges on the molars or more complicated, such as jaw alignment issues. Advances in nutrition, parasite control, and preventative medicine have greatly improved life expectancy in horses. Their teeth, however, still only last so long. By about age 28-32, many horses start losing teeth. With regular dental care, we can keep these horses more comfortable and hopefully lengthen the time that they have useful teeth. Eventually, if horses outlive their teeth, special feed that is easier to chew will be required, such as a complete senior feed or hay pellets.

Older horses aren’t the only ones with dental issues. Over the years, we have bred horses for many purposes, including good leg conformation, speed, strength, and yes, color, but not much emphasis has been placed on good teeth. Starting early with dental exams can help identify potential issues before they become problems. Alignment issues and abnormal wear patterns are much easier to deal with early on. Because they continue to erupt throughout life, uneven wear can lead to future problems such as wave mouth, which is impossible to correct if severe enough. Regular dental care may even save money on feed bills, due to better feed conversion and less grain dropping on the ground.

Parasites

Each parasite has its own way of bringing down the health of the horse. Some parasites feed on the blood; some damage the intestinal lining, preventing normal absorption of nutrients; others migrate through the lungs or other organs, destroying normal tissue as they go. In any case, the horse is less healthy and less productive when it has parasites.

The good news is that most parasite infestations are easy to diagnose. A simple fecal floatation test can detect most internal parasites, and most of the external parasites such as lice and ticks are seen with the naked eye. What to do about these can be more complicated. Treatment and prevention is best discussed with your veterinarian.

Everything Else

Infectious disease, cancer, metabolic abnormalities, ingestion of toxic plants: these are just a few entries on the long list of problems that can cause weight loss in horses. Diagnosis starts with a basic physical exam and complete history. More complicated cases may require blood work, cultures, or other laboratory tests.

With any weight loss case, an accurate history is imperative. Often, the answer is found before the horse is even seen. Keep accurate weights on the amount of hay and grain that is fed daily. Regular visits by your veterinarian can help with early detection of dental and health problems. And let me say again: Weigh your feed! Coffee cans are not a measure of weight!