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Grazing horses prone to laminitis

Quick facts

  • High amounts of sugars in grasses can bring about laminitis in horses susceptible to the disease.
  • Susceptible horses should have limited grazing or no grazing.
  • If you do graze, do it between 3 a.m. and 10 a.m.
  • Carefully select pasture plants.
  • Watch the weather.
  • Don’t overgraze pastures.
  • Use a grazing muzzle.
  • Keep the horse in shape.
  • Work with a veterinarian and nutritionist.

Founder or laminitis, is swelling of the tissues that connect the hoof wall to the coffin bone. Signs of founder include:

  • Signs of pain in the feet.

  • Increase digital pulses in the lamina.

  • Swelling in the lamina that may cause the coffin bone to rotate or sink.

Often, laminitis relates to nutrition and diet. Rapid intake of nonstructural carbohydrates (or sugar) stored in pasture plants can cause laminitis. Cool season grasses like orchardgrass, bromegrass, and timothy tend to store more carbohydrates.

Is your horse prone to laminitis?

High sugars found naturally in Minnesota forage species can trigger pasture-caused founder in susceptible horses. Susceptible horses include, but aren’t limited to:

  • Overweight, easy keeping horses.
  • Ponies.
  • Horses with metabolic syndrome.
  • Horses that have foundered before.

Grazing susceptible horses

Susceptible horses should have limited grazing or no grazing at all. For extremely sensitive horses, there is no completely safe time to graze. Not all horses need to follow these recommendations, but susceptible horses should. Grazing during these times or scenarios doesn’t guarantee the sugar content will be lower.

Sugar (carbohydrate) content is highest:

  • In immature grass (early spring and during re-growth).

  • During periods of cool nights and warm sunny days (fall or early spring).

  • After a hard freeze.

  • During drought conditions.

When should susceptible horses graze?

Susceptible horses should graze when forages are lower in sugar. Many factors affect the amount of sugar present in forages including:

  • Weather
  • Plant stress
  • Species maturity (the plant’s stage of growth)
  • Time of day
  • Time of year

During daylight hours, grasses make and store sugars as they take in water, sunlight and carbon dioxide (photosynthesis). Plants use sugar to fuel growth overnight. So plant sugars are higher in the late afternoon and lower in the early morning. Susceptible horses should graze between 3 a.m. and 10 a.m., when plant sugars are lower.

Plants collect sugar in times of stress such as during a drought or when temperatures fall below 40° F. Don’t graze susceptible horses during periods of plant stress.

Minnesota’s cool spring and fall weather may also cause plants to collect sugar. This may increase the risk of pasture-caused laminitis for susceptible horses. Warmer weather or dark periods (night hours or cloudy days) offer better times to graze as plants are using sugars for quick growth.

Overeating

Overeating can still cause disease in susceptible horses. Horses grazing in areas shaded by trees or buildings may be able to graze longer as plants will be collecting less sugar. Allowing pasture grasses to become more mature should also reduce the sugar content and result in less (and a slower) eating.

Grazing muzzles

If grazing is your horse’s main source of exercise, consider using a grazing muzzle. Grazing muzzles limit the amount of forage a horse can eat.  

Exercise

Regular exercise and good body condition will help lower the risk of pasture-caused laminitis.

Managing pastures 

Seek veterinarian approval before grazing horses prone to (or with previous episodes of) laminitis. If you have a sensitive horse, you must manage pastures carefully.

  • Don’t overgraze.

    • The lower part of a plant may contain the highest amount of sugar.

  • Avoid grazing pastures with a lot of seed heads.

    • Seed heads can contain high amounts of carbohydrates.

  • Limit grazing during times of environmental stress on plants (e.g. drought).

  • Gradually introduce horses to lush spring pasture.

Pasture species

Some pasture species are more likely to collect sugar under stressful conditions than others.

Species more likely to collect sugars include:

  • Timothy
  • Bromegrass
  • Orchardgrass
  • Most cool season grasses in Minnesota horse pastures

Most forage species store sugars in the bottom 34 inches of growth. Making sure pastures are not overgrazed will help avoid laminitis. Correctly fertilize pastures and avoid grazing susceptible horses during times of plant stress.

Control weeds

Recent research doesn’t directly link eating weeds to laminitis. But the wide range of nonstructural carbohydrate content within weed species suggest horse owners should control dry lot weeds. This is especially true for owners with laminitic horses and ponies.

Krishona Martinson, Extension equine specialist

Reviewed in 2020

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