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Unrein advises owners to restrict horse’s access to fresh green grass

by Wyoming Livestock Roundup

Douglas – “The grass is so green this year that if a horse is not used to being turned out on such green grass, they could end up with grass founder,” states Brenda Unrein, veterinarian at Veterinary Associates in Wheatland. 

Founder is sometimes referred to as laminitis, and it is the result of inflammation of the laminae in the horse’s foot.

“Please don’t turn horses out to green grass and let them eat all that they can hold,” she adds. “Owners will be calling their vet because their horse won’t be able to walk.” 


“In a horse’s foot there is the hoof and the bone,” comments Unrein. “In between the hoof and bone there is laminae. It holds those two things together in the correct position on the front part of the horse’s hoof.”

She further explains, “On the back side of the horse’s hoof, there is a tendon called the deep digital flexure tendon. This tendon contracts and pulls on the hoof and bone. This equilibrium keeps the horse’s hoof and bone in the right alignment.”

“With laminitis, the laminae becomes inflamed and pulls apart on the front and around the side of the foot,” describes Unrein. “However, the pulling of the back of the foot by the deep digital flexure tendon never stops, and a rotation of the bone in the hoof occurs.”


Unrein noted the rotation of the bone is often referred to as “rotation” or “sinking” with foundered horses. 

“Eventually, if there is enough inflammation in the laminae and it completely pulls apart, the rotation of the bone will continue, and the bone can come through the bottom of the horse’s foot,” she adds. 

To show rotation in a horse’s hoof an x-ray needs to be taken. Unrein explains that the bone and hoof wall of a horse should be parallel.

“When the bone rotates, the amount of rotation is measured in degrees,” she explains. “We monitor a foundering horse’s progress by the degrees of their bone rotation to see if we are making any headway or not.”


“The rotation of the bone can be stopped, but it can never be reversed, that’s the bad part,” describes Unrein. “Once a horse has laminitis, sometimes they are more prone to further inflammation of that laminae and separation from their hoof. It’s not a great disease to watch.” 

Unrein mentions that she sees several cases of grass founder every year, and she is not always able to save the horse. 

“Sometimes we are unable to stop the process of the bone rotation, no matter how hard we work or what we do,” comments Unrein. “The sooner an owner calls their vet when they notice something is not right with their horse, the sooner we can get results of what is wrong with them.”

Grass founder

The main causes of founder are when a horse consumes too much grain or green grass and when a horse has colic.

“Grass founder is from really lush, green grass,” says Unrein. “It’s the carbohydrates and sugars in the green grass that causes the inflammation in the horse’s feet and causes the laminae to pull apart.” 

She continues, “When grasses are first coming up, they are full of sugars. Older grasses, like the grasses from the winter and fall, are safer to eat.”

Unrein further notes the horses most prone to grass founder are those that are already overweight. A big, thick neck that has a cresty appearance, a very wide back that can hold water on their topline and lack of shed of their hair are all characteristics of overweight horses. 

However, any horse can contract grass founder. 


“I tell people that before they turn their corral horse out to pasture to feed them first and then only turn them out to the green grass for 15 minutes for the first three to four days,” comments Unrein. “Don’t turn them out for days.”

“Slowly build their time out with the green grass,” she continues. “The reason I tell people to feed their horses first before turnout is because their horses will be full, and when they go out to the pasture, they will only pick at the green grass, not ravish it.” 

Unrein mentions that after a few days of 15-minute turnouts, the amount can be increased to 30 minutes for a few days and eventually built up to a couple of hours where horses can graze the green grass.  

Unlimited access

“For horses that are turned out all the time owners won’t have to limit their access to the green grass,” states Unrein. “The horses will eat all of the green grass as it comes up, and when that is all gone they have to go back to the old grass.”  

She adds, “Horses that are out all the time adjust themselves to the new green grass.” 

Unrein spoke at the Big Wyoming Horse Expo, which took place April 25-27. Madeline Robinson is the editor of the Wyoming Livestock Roundup and can be reached at

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