What is Equine Laminitis?

Equine laminitis is a common, painful condition of the equid foot that can affect horses, ponies, donkeys, and mules.

The horse’s foot is made up of an outer hoof wall, an inner bone known as the pedal bone, and two sets of laminae that hold the bone in place inside the hoof. The laminae are finger-like projections. One set is on the outside of the bone and the other on the inside of the hoof wall. Those interlock with a large surface area to withstand the forces of the horse’s weight pushing down on the pedal bone. They also resist pressure of the flexor tendons that run up the back of the leg that are pulling on the pedal bone.

What Is Laminitis?

There are three types of laminitis:

Sepsis-associated laminitis. This occurs in sick animals with severe diseases affecting the gastrointestinal system (e.g., diarrhoea or colic in which part of the intestines have become strangulated), the lungs (e.g., pleuropneumonia or shipping fever), or the uterus (e.g., if the placenta is not passed after foaling and an infection develops).
Supporting limb laminitis. This occurs when the horse is very lame on one leg (e.g., has broken their leg or has a joint infection) and spends all of its time putting the weight on the other leg. The other leg is at risk of developing laminitis through a lack of blood flow.
Endocrinopathic laminitis. This is the most common form, accounting for about 90% of laminitis cases. It occurs in animals with one of the two most common endocrine (hormone) disorders that occur in horses, namely equine metabolic syndrome (EMS) or pituitary pars intermedia dysfunction (PPID, also known as equine Cushing’s disease).

What Happens in Equine Laminitis?

When laminitis occurs, the bond between the two sets of laminae become inflamed (in sepsis-associated laminitis) or weakened (in supporting limb and endocrinopathic laminitis) such that the pedal bone is no longer held firmly in place within the hoof.

The weight of the horse pushing down on the pedal bone means that it might sink toward the sole inside the hoof. And the pull of the flexor tendons means that the pedal bone might rotate so that the tip of the pedal bone heads toward the sole.

All of this is very painful for the horse and results in lameness affecting usually two or more feet.

As well as lameness, the hoof wall might feel warmer than usual, the pulse to the foot (digital pulse, felt at the level of the fetlock or the pastern) is increased or bounding, and the horse might lean back on its heels to take the weight off the more painful toe area of affected feet.