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Extension > Agriculture > Livestock > Horse > Horse care and management > Caring for the underweight horse

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Caring for the underweight horse

Marcia Hathaway, Devan Catalano and Krishona Martinson

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.

Body condition score

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

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 Animal Nutrition’s website. To learn how to figure out your horse's body condition score watch our video.

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:

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.

  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

Table adapted from 2007 Nutrient Requirements of Horses.

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:

Age

Many older horses have worn or missing teeth, which can make chewing forage hard. In addition, as horses age, their digestive tracts change. These changes make it harder to digest and absorb nutrients from their food, especially hay. As a result, older horses may need a type of feed known as a “complete feed”.

Complete feeds:

Older horses often also need more time to eat and drink, and may need periods of rest between meals. You may need to separate older horses from the herd to make sure they’re eating and drinking enough. You should also have an equine dentist examine your senior horse twice a year to check for and correct any tooth problems that might interfere with chewing.

Environment

Pecking order

Horses low in the pecking order may not have adequate access to hay, other feed products and water. If you can’t separate the horse from the herd for meals, try using a feed bag that attaches like a halter. A feed bag will give them time to eat their ration without getting pushed away from it.

Poor water intake

If a horse’s water intake is lower than usual, their feed intake will also slow down. Provide fresh, clean water between 45 and 65 F to encourage horses to drink. Place water sources near the horse, as horses often limit how far they are willing to walk for water. The average adult idle horse in a mild climate will consume about 10 gallons of water each day.

Unwanted behaviors

Stall walking, weaving, cribbing, and fence pacing all burn calories. Trying to address these unwanted behaviors or feeding hay in a hay net may distract the horse from performing the unwanted behavior.

Insects and pests

In the summer, horses may not get enough grazing or eating time due to bothersome insects. Insecticides and protective sheets will help limit the impact of these pests.

Climate

Hot weather

Feed intake will often decrease as air temperature and humidity increase. Digestion creates body heat from fiber in hay and pastures. Because forages contain more fiber than grains, forages produce more heat. As a result, it’s natural for horses to eat less forage during hot periods. Offering hay during cooler parts of the day can help. You may need to feed additional grain products during hot periods to meet the caloric needs of an underweight horse if they refuse hay.

Cold weather

Horses need more hay in the winter to keep warm. Horses may also need extra grain during more severe winters.

The lower critical temperature (LCT) is the temperature below which a horse needs additional energy to keep warm. All horses have a LCT threshold, which is about 18 F. This threshold can differ between horses, based on the climate a horse is used to.

For each 1 F drop below the LCT, a horse requires a 1 percent increase in energy or about two pounds of hay. Some horses may require up to 50 percent more calories in extreme cold. Whenever possible, additional calories should first be met by feeding more hay. Forages are higher in fiber, producing more heat than grains. Thus, forages will aid in maintaining body temperature and weight.

Wind, rain and snow greatly affect the horse’s body temperature. Keep your horse’s blanket and hair coat dry. In the presence of wind, wet horses will have trouble keeping warm and may lose body weight.

Several factors that can lessen these affects include:

Health

Some horses may be underweight due to more serious health problems. These horses should be treated by a veterinarian, farrier or equine dentist, depending on the health issue.

Health problems that may result in an underweight horse include:

Check your horse weekly for body condition, health issues and injuries.

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