How to Keep Weight on a Horse: Managing the Hard Keeper

Updated June 27, 2023
Thin thoroughbred horse in a paddock

Did your horse come out of winter a little thinner than last year? Horses lose weight for a variety of reasons—some of them medical, some of them man-made. Find out why your horse may be underweight and what you can do about it.

Potential Causes of Weight Loss in Horses

First, have your veterinarian perform a complete physical examination on your thin horse to rule-out any medical diseases or conditions. As you can see from this list, there are some common health reasons for horses to lose weight, like parasites, and there are some uncommon reasons, like cancer. Some of the more uncommon ones will need additional testing to reach a diagnosis. Each medical reason has one or more examples to help explain why weight loss can occur:

  • Malnutrition – parasites, poor dentition
  • Malabsorption – disorders of the small intestine
  • Protein-losing gastroenteropathy – stomach ulcers
  • Acute diarrhea – Potomac Horse Fever
  • Chronic diarrhea – sand in the intestine
  • Chronic pain – severe arthritis or laminitis
  • Chronic infection – abscess, peritonitis
  • Organ failure – kidney or liver disease
  • Metabolic disease – Cushing’s Disease
  • Cancer

Of course, there are non-medical reasons why horses are underweight, and those can be divided into four categories: nutrition, living environment, age and breed/genetics, and their training or use.


There’s a term veterinarians use when a horse is thin simply because he’s not getting enough quality food to eat: "agroceriosis" or, lack of groceries. Step back and really examine the forage and grain your horse eats. Is the hay from two years ago and does it look more like straw? Is the one-acre pasture for both horses mostly weeds? Is your grain from a small, local source that may or may not understand proper horse nutrition?

Now think about how much your horse eats. Is he getting 1.5 – 2.0 % of his body weight every day in food? (For a 1200-pound horse that 24 pounds of hay and grain to be divided into two or more feedings). Is he getting at least as much grain as the label on the bag says? Are there long periods of time during the day when he has no food in front of him?

Living Environment

If you think you’re doing everything right when it comes to the feedstuffs you give your hard keeper, now consider if there is any stress in his life that you can eliminate. For example, does he have to compete for his share of hay and grain with the herd? Is he constantly having to dominate or submit to other horses in his herd? Does he spend most of his time in a stall? Does he travel and compete frequently? Does he have relief from sun, bugs and heat in the summer and precipitation and cold temperatures in the winter?

Age, Breed and Genetics

As horses age into their teens and twenties, their bodies begin to function less efficiently. However, this does not mean older horses are supposed to be or have to be thin. It just means they may need more veterinary care and improved management to properly manage their weight. The Henneke Body Condition Scoring chart, which is a scale from 1 = emaciated to 9 = obese, considers the fat and muscling a horse has over certain parts of his body, not his age. The same is true when body condition scoring a breed that always seems to have trouble keeping weight on, such as thoroughbreds.

Training or Use

Next, bear in mind what calories you’re asking your horse to burn. Is he only used for occasional trail rides? Does he get ridden lightly four to five days a week? Is he on a heavy training and competition schedule? Remember that some horses, especially older ones (and thoroughbreds at that), do a better job of keeping up their weight if given some controlled exercise beyond just turnout. Hacking on a long rein, lunging or even hand walking up and down hills or over cavalettis may help add muscle to an inactive but thin horse.

Supplements That May Support Weight Gain

Fat can be safely added as an additional source of calories. Look for a product with essential fatty acids, especially omega-3s. Help build muscle with amino acids such as lysine, methionine and threonine. Newer ingredients such as gamma oryzanol, creatine and HMB may also be of benefit in muscle development. Stimulate appetite with the herb fenugreek, bee pollen or the number one flavor horses prefer: banana! Finally, improve overall digestive health with pre- and probiotics, enzymes, and intestinal protectants such as l-glutamine and licorice.

SmartPak strongly encourages you to consult your veterinarian regarding specific questions about your horse's health. This information is not intended to diagnose or treat any disease, and is purely educational.