Obese Horses Most Susceptible To Grass Founder

Lush spring grass increases the chance of founder in horses.

Actually founder, officially known as laminitis, can be caused by many different conditions, including overeating, taking on large amounts of water, hard riding and   problems at foaling.

“Grass founder is a
form of overeating, but is actually a merging of two conditions: obesity and a new supply of highly digestible grass,” according to Dr. Robert Leonard, veterinarian at West Plains, Missouri.

“If the horse is in working condition, it is very unlikely to founder on new grass,” Leonard pointed out. “The obese horse, on the other hand, can founder on good quality hay or summer grass that has gone to seed.

“The heavy horse has a threshold where it is safe.  This is when its nutrient intake matches the energy needs of its body,” Leonard continued.

As the level of a horse’s activity slows, so does the body’s machinery, which further reduces the need for energy.

“The heavy horse has become so efficient he is able to store a great deal away in the form of fat,” Leonard described.  “These storage areas can be seen over the ribs, across the rump, and most conspicuously forming a crest along the top of the neck. But, the horse just keeps on eating.”

After a winter of hay and little grain, the new grass looks very appealing. “It is also much more digestible than hay and pushes the horse over the threshold,” Leonard said. “After a few hours of grazing, the body starts to react to the new grass like it
would any foreign substance.

“This allergic reaction results in restriction of blood flow to the feet, which limits the
oxygen supply to the tissue,” Leonard continued. “Without oxygen, the cells die and the tissue starts breaking down, allowing the coffin bone to pull away from the hoof wall.”

The coffin bone is connected by tendons to the rest of the leg. These tendons run from that bone up the back of the leg to various muscles and are the ones flexing the leg when the horse walks or runs.

“Each time the foot makes contact with the ground, the tendons are drawn tight,” Leonard related. “Normally this gives spring to the step as the coffin bone is firmly attached to the hoof wall.  But common with inflammation of the foot, the tendons
actually add to the discomfort by pulling the coffin bone away from the hoof.”

The longer the toe of the hoof, the greater the break over a period of time, which keeps tension on the coffin bone longer. A shorter toe allows the foot to break over more quickly and before the tendons are drawn tight. Horses can be encouraged to
lie down to relieve pressure on the hooves.

“Treatments include administering antibiotics to fight infection, antitoxins to reduce bacterial toxicity, anticoagulants and vasodilators to improve blood flow to the feet,”
Leonard prescribed. “Painkillers and anti-inflammatories for your horse are also usually necessary.”

“A delay of even a few hours can literally be the difference between continued healthy living and euthanasia,” Leonard warned

As soon as the horse has been treated for the acute phase of founder, owners must turn attention to the hoof.

“Trimming the toe very short will allow more comfortable walking,” Leonard advised.  “In more severe cases, shoeing with a flat shoe, and preferably one with a worn toe, will protect the foot from contact with the ground.”

Additional doses of pain reliever or local nerve blocks may be necessary before the farrier can work on one foot while the horse supports all its weight on the other.

As the grass starts to respond to fall rains, horses can eat themselves into trouble

“They become even more susceptible and should be placed in a dry lot and fed low quality hay,” Leonard commented. “The roughage is essential for intestinal function, but hopefully the horse will burn more calories digesting it than it will provide.

“Exercise, diet restriction, a serious illness, or nursing a foal are the only ways to slim   down the horse who has become obese,” Leonard concluded.