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Caring for the underweight horse

It’s rare to see a healthy horse that’s too thin since thin horses may be at higher risk for health problems. Before setting up a feeding and management plan for a thin horse, determine why the horse is thin by working with an equine veterinarian and nutritionist.

Determining if your horse is underweight

The two most common ways to assess your horse’s body condition and body weight are body condition scoring and ideal body weight equations.

drawing of a horse with identifiers to use in assess body condition score.
Six areas to assess body condition score

Body condition score

Body condition scoring (BCS) evaluates the fat deposit under the horse’s skin in six areas.

  • Neck
  • Withers
  • Behind the shoulder
  • Along the back
  • Rib area
  • Tail head

BCS uses the Henneke scale: 1=poor; 9=extremely fat. The ideal BCS for most breeds and disciplines is 5, but ranges from 4 to 6.

A horse with a score of 4 is considered healthy, but it’s important to look at the overall picture. Has this horse lost body weight and dropped from a score of a 5 or 6 to a 4? Is it an older horse or one without a good hair coat going into winter? These may be reasons to put body weight on a horse.

Horses scoring 3 or lower are underweight or thin. In situations of extreme neglect or poor health with a horse that scores 1 or 2, we recommend working with a veterinarian or equine nutritionist to create a re-feeding plan.

For more information on body condition scores visit Purina's Animal Nutrition website.

Learn how to figure out your horse's body condition score

Ideal body weight equations

Researchers at the University of Minnesota developed ideal body weight equations to help determine your horse’s ideal body weight based on his or her overall frame.

To calculate your horse’s ideal body weight you need the following measurements:

  • Height, from the top of the withers
  • Body length, from the point of the shoulder to a line perpendicular to the point of the buttock. Don’t wrap the tape measure around the buttock.

Calculating ideal weight for different horse breeds

Horse breed type Ideal weight equation
Arabian ((Length × 23.52) + (Height × 15.58)) − 1,344
Draft ((Length × 27.55) + (Height × 25.98)) − 2,092
Miniature (3+ years) 23.25 × (Length 0.79 × Height 1.74) /868
Miniature (<3 years) 33.92 × (Length 1.92 × Height 1.26) /18,209
Pony ((Length × 23.52) + (Height × 15.58)) − 1,333
Saddle-type 20.34 × (Length 1.37 × Height 1.01) /359
Stock ((Length × 23.52) + (Height × 15.58)) − 1,269
Thoroughbred ((Length × 10.69) + (Height × 23.76)) − 1073
Warmblood ((Length × 27.55) + (Height × 25.98)) − 2,235

Causes and possible solutions

Not enough calories

The horse’s digestive system makes forages their ideal source of energy. Thus, you should minimize or avoid feeding large amounts of grain if possible.

If your horse is thin without any underlying health issues, and simply needs more calories, you can fix the problem by:

  1. Allowing 24/7 access to pasture or hay (or as much forage as possible).
  2. If increased amounts of hay aren’t enough, try offering a higher quality hay such as alfalfa or an immature grass hay.
    • Alfalfa tends to be higher in energy and protein and lower in sugar.
    • Alfalfa can be fed as hay or as cubes/pellets.
  3. If you aren’t feeding any grain, try adding a grain product meant for working or performance horses.
    • These grains will contain higher levels of protein and fat that will aid in body weight gain.
  4. If you are already feeding grain, instead of feeding more, try switching to a performance feed product with 10 to 12 percent fat.
    • Using fat to increase the energy in a ration can help reduce temperament changes seen in some horses eating large amounts of starch or carbohydrates.
  5. If you are unable to change the grain product, add a high-fat supplement to your horse’s regular ration such as:
    • Rice bran
    • Flax seed
    • Vegetable oil
    • Dried granular fats

More information on feeding horses for weight gain can be found on the Purina nutrition site.

Make gradual changes in feed

Make all feed changes gradually over a two-week period to allow enough time for the gut to adjust to the change. Feed for a weight gain of 0.5 to 0.75 pounds daily. Three to four pounds of an additional grain product can meet this gain if the horse's body weight is stable. Use the table below as a guideline.

Horses take about three weeks to adapt to a high fat diet. Introducing a high-fat diet too quickly can cause greasy feces or diarrhea.

Table adapted from 2007 Nutrient Requirements of Horses.
Maintenance Light work Moderate work Heavy work
Grass hay 20 lbs 20 lbs 21 lbs 22 lbs
Grain ration 4 lbs 6 lbs 9 lbs 12 lbs

Other reasons your horse might be underweight

Health problems are common causes for underweight. Consult a veterinarian or equine nutritionist to find the exact cause, which may include:

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Marcia Hathaway, Devan Catalano and Krishona Martinson

Reviewed in 2018

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