Laminitis

Laminitis is known by a few names, usually “founder” (which comes from the way these horses walk when their feet are very sore) or “fever in the feet” (because the hooves can become quite hot). To break it down, laminitis means “inflammation of the lamina”.  So what is a lamina?

The hoof of a horse is comprised of a few layers.  The deepest layer is the coffin bone, or the third phalanx.  Wrapped around the coffin bone is a connective tissue layer called the “sensitive lamina”, and wrapped around that is another connective tissue layer called the “insensitive lamina”.  The insensitive layer is firmly attached to the inside of the hoof wall.  The two layers of lamina – sensitive and insensitive – hold on to each other through lots of little projections which interdigitate.  So basically, the coffin bone is being held inside the hoof by these Velcro-like attachments of the two layers of lamina.

When the lamina becomes inflamed, the attachments between the two layers start to loosen.  The deep digital flexor tendon, which attaches at the bottom of the coffin bone, then begins to pull the front (or “toe”) of the coffin bone downward, towards the sole of the hoof.  This creates “rotation” of the coffin bone within the hoof capsule.  The other type of “movement” that can be caused by this loosening of the lamina is “sinking” of the bony column.  This means that the whole coffin bone (and everything above it) sinks down into the hoof.  Both types of movement can happen in the same horse, often at the same time.  We can measure both rotation and sinking on radiographs.  

Cause

Laminitis results from the disruption of blood flow to the sensitive and insensitive laminae within the foot, which secure the coffin bone (P3) to the hoof wall. While the exact mechanisms by which the feet are damaged is still being determined, certain precipitating events can produce laminitis.

Concussive Trauma

Concussion (“road founder”) is the easiest cause to understand – riding for long stretches at high speeds over hard ground can cause concussive trauma to the feet, damaging the lamina.

Increased Weight Bearing

An injury or trauma that causes the horse to bear less weight on one leg may also induce laminitis in the supporting limb, as in the infamous case of Barbaro. The continuous increased stress placed on the weight bearing limb strains the lamina that hold the coffin bone stable in the hoof, resulting in inflammation and laminitis. It is important to provide support and cushioning to all feet and legs for a horse being treated for any injury or lameness that changes how it bears weight.

Systemic Disease

Although laminitis occurs in the feet, the underlying cause is often “systemic”, meaning a disturbance elsewhere in the horse’s body. The lamina are easily affected by any fever, toxin or metabolic disease…likely because they are such a delicate, intricate system which supports such a huge weight.  In the late spring time, we particularly worry about the horses with metabolic diseases – Cushings, Equine Metabolic Syndrome, Insulin Resistance, etc.  We consider these horses as more prone to laminitis, even if they have never experienced the disease before.  

Recent research has led to the description of the laminae in a horse’s foot as a ‘shock organ.’ That is, an organ that fails related to some sort of systemic disease. This suggests that by treating other diseases more effectively — like colitis, or a mare with a retained placenta, or a horse with pleuropneumonia — we can better protect the foot from becoming the shock organ that ultimately fails and results in a crippling disease.

Carbohydrate Overload

Laminitis can also occur after a carbohydrate overload, where your horse eats too much rich young grass or grain. This is why, although laminitis flares are not restricted to a specific season, veterinarians tend to see increased cases in Spring.

Clinical Signs

As a horse owner, it is important to recognize the signs of laminitis and seek veterinary help immediately.

Signs of acute laminitis include the following:

  • Lameness, especially when a horse is turning in circles; shifting lameness when standing

  • Heat in the feet

  • Increased digital pulse in the feet

  • Pain in the toe region when pressure is applied with hoof testers

  • Reluctant or hesitant gait, as if “walking on eggshells”

  • A “rocking horse stance” in the front, with the front feet stretched out in front to alleviate pressure on the toes

Signs of chronic laminitis may include the following:

  • Rings in hoof wall that become wider as they are followed from toe to heel

  • Dished hooves, which are the result of unequal rates of hoof growth

  • Thick, “cresty” neck and abnormal fat deposits (signs of metabolic disorders that often cause laminitis)

  • Bruised soles or “stone bruises”

  • Widened white line, or “seedy toe,” with occurrence of blood pockets +/- abscesses

  • Dropped soles or flat feet

Treatment

If you suspect laminitis or your horse has gotten more than a normal amount of carbohydrates (grass or grain), consider it a medical emergency and notify your veterinarian immediately. Early intervention in acute laminitis carries the best prognosis. The sooner treatment begins, the better the chance for recovery.

Your veterinarian may recommend icing your horse’s feet if it is an acute case, and placing him on deep, soft bedding with no or limited grain and lower quality hay until they are able to see them. They may also recommend applying cushion/support to your horse’s feet via boots or pads made of foam insulation sheets and duct tape.

Treating laminitis requires a multi-modal approach. Your veterinarian will need to work closely with your farrier to develop a plan and identify any changes to the coffin bone-hoof structure. X-rays may be needed to look for rotation and/or sinking of the coffin bone. Close communication between your veterinarian, farrier, and yourself is essential to prevent any further changes from occurring while keeping your horse comfortable during recovery.

Prevention

The most important thing is to prevent the causes of laminitis, and if signs occur, to REMOVE the cause (if known).  In the case of horses with metabolic issues, treating the metabolic disease is often the first step in prevention and/or treatment.  Your veterinarian can help you in the diagnosis and treatment of these diseases/syndromes.  And be aware of when the grass is most lush (sugary) – spring is a common culprit, but fall can also be dangerous, especially when the grass goes through a few “freeze-thaw” cycles.  Grazing muzzles can help decrease the amount of grass your horse can take in.  Some horses with severe metabolic disease cannot tolerate any fresh grass, and must be kept on a “dirt lot” to prevent grazing.  Be aware that some types of hay are more “sugary” than others; alfalfa hay is commonly quite rich, but some very “green” regular grass hay can be very rich as well.  If you’re worried that your hay is too rich for your horse, soaking it in cool water for 30 minutes prior to feeding may leach out some of the simple sugars, making it safer to feed to at-risk horses.