Laminitis. The word alone is enough to send shivers down any equestrian’s spine. Often deemed as a death sentence, laminitis is one of the most common disorders in horses and ponies. Laminitis is defined as inflammation of the tissue between the hoof and coffin bone.
Contrary to many people’s beliefs, founder and laminitis are not synonymous. In severe cases, laminitis may PROGRESS to founder, wherein the coffin bone can rotate downward causing severe pain for the horse.
As far as statistics go, fifteen percent of adult horses will be afflicted with laminitis sometime in their lives. Twenty to thirty percent of those horses will develop debilitating and re-occurring symptoms which in five percent of cases lead to euthanasia. But what exactly is laminitis and how is it caused? How can I prevent this horrible disorder?
To answer these questions and more, I would like to start with a detailed look at the anatomy and physiology of the equine hoof.
Anatomy and Physiology of the Hoof
First and foremost, the equine hoof is truly an amazing structure. Just think about it. All that weight is supported on the four tiny points that are the hooves. So how exactly have these structures developed to help distribute all that weight?
When a horse walks or even stands, weight is pressed down and spread through to the hoof wall, which flexes slightly. Why is this? One, this allows the hoof to absorb shock and concussion when moving. Two, the flexing acts as a pump to move blood throughout the foot and leg.
When looking at the bones of the hoof and lower leg we see the long pastern (P1), short pastern (P2), and coffin bone (P3). The deep digital flexor tendon (DDFT) runs down the back of the leg and connects to P3. This tendon is responsible for the flexion of the lower leg.
It is important to note that there are no major muscles in the lower leg — merely tendons, ligaments, and bones. The sole of the hoof is not weight-bearing as the coffin bone rests there, as seen in the diagram below.
The hoof attaches itself to the bone via numerous toothbrush-like bristles called laminae. On the underside of the hoof, we have insensitive laminae and on the bone side, we have sensitive laminae. These two types of tissues mesh together and hold the hoof to the bone as illustrated below at a microscopic level.
Causes of Laminitis
As stated above, laminitis occurs when these laminae become inflamed and painful. This causes the horse to exhibit the main symptom of laminitis — leaning backwards.
Although we are not one hundred percent certain why laminitis occurs, there are a few common causes that we will discuss below.
Sepsis
Sepsis is defined as a systemic inflammatory response to infection. There are a few common ways horses can get sepsis: enterocolitis, pneumonia, and retained placenta.
Enterocolitis occurs when there is inflammation and infection in the horse’s intestines whereas pneumonia is a major infection in the lungs. Things get a little more complicated when looking at a retained placenta.
When a horse goes through parturition (having a foal), they are meant to pass the foal followed by the placenta. Broodmares can take up to three hours to pass the placenta — any longer and the mare is at risk of infection.
If not passed, the placenta begins to degrade inside the horse’s body and causes a major infection. Laminitis is often right behind this infection causing the horse even more distress and pain.
Typically, a veterinarian will administer oxytocin to try and help the mare pass the placenta and avoid infection.
Endocrinopathy
Endocrinopathy can essentially be described as a hormone imbalance in the horse. This cause is one that most equestrians are probably familiar with. Numerous conditions can lead to an imbalance:
- Improper insulin regulation
- Hyperinsulinemia (Pituitary Pars Intermedia Dysfunction) – aka Cushing’s Disease – caused by a tumor in the brain
- Equine Metabolic Syndrome – inability to regulate blood insulin levels (often seen with a cresty neck)
- Obesity – most often seen in ponies
- Carbohydrate overload – horses get out of the stall and consume a large amount of grain
- Adipose (fat) tissue dysfunction (not necessarily associated with obesity)
- Overproduction of adipokines (cytokines, produced by adipocytes)
All of these conditions cause a perpetual state of inflammation, changes in blood flow, and overactivation of matrix metalloproteinases (MMPs). MMPs are enzymes that help degrade different kinds of cells in the body.
Fortunately, these causes are typically controlled through management adjustments (diets, more exercise, pharmaceutical therapies, etc.).
Trauma
Next, we have trauma laminitis which is also known as “mechanical” laminitis. This cause can occur from habitual pawing, riding on a hard surface repetitively, or from support limb laminitis.
Habitual pawing is typically caused by horses that are not allowed proper turnout. This can lead to boredom and frustration and therefore pawing. The constant concussive action can cause inflammation and therefore laminitis.
Riding on hard surfaces frequently without proper protection (shoes or proper rest) can also lead to concussive laminitis over a prolonged period of time.
Support limb laminitis can occur when a horse has injured one leg and is habitually resting on the opposite leg. The injured leg alters the normal weight-bearing process and can lead to laminitis as well.
Founder in Horses
It is important to note that founder and laminitis are NOT THE SAME. Founder is simply the result of untreated laminitis. It is impossible to have founder without laminitis. But how does founder occur?
In all of the aforementioned cases, there are a few physiological tendencies that help with the assault on the equine body. Since inflammation is occurring, there is a build-up of blood. Along with this increased blood flow, MMPs arrive and can begin to degrade the soft tissue (laminae) in the area.
Now, as you may remember from before, these laminae layers are the only thing that is keeping the hoof and bone connected. When the MMPs begin to degrade the tissue, the insensitive and sensitive laminae begin to separate.
This means there is no longer any support for the coffin bone. The toe is no longer pulled forward and the DDFT begins to pull on the coffin bone causing it to rotate down towards the sole.
This process can take weeks to happen and is usually identified through an x-ray. If the coffin bone has rotated too far, it is our ethical duty to euthanize the horse as there is nothing that can be done for them.
Once a horse has foundered, they are most certainly going to founder again.
Prevention of Laminitis and Founder
Surprisingly, the best corrective measure for laminitis and founder is to not need one! Prevention is key! Depending on the severity of the case, treatment can be very expensive and hard for the horse. Luckily, there are a few management changes equestrians can make to help prevent laminitis from occurring.
Feeding
Simply maintaining your horse’s ideal bodyweight/body condition score can help keep your horse safe. Here’s a few tips to help you achieve this:
- Put grazing muzzles on at-risk horses in the spring and possibly for the entire grazing season
- Make sure your horse gets enough exercise
- No overfeeding or giving excessive amounts of high-sugar feed or treats
- Ensure that feed bins are securely closed and/or locked
Hoof Management
Next, another step that you can take is to perform regular hoof inspections. Check to be sure there is no increased hoof pulse or warm hooves. Does it look like your horse’s hoof is getting the proper support?
Make sure that your horse is getting regular and proper hoof trimmings. The equine hoof grows 1/4″ to 1/2″ per month. If the toes are allowed to grow long, pressure is placed on the DDFT which can lead to coffin bone rotation.
Environmental Management
Ensure that you are checking your horse’s environment (stall/pasture) for any signs of black walnut trees or shavings. Black walnut is a hoof irritant and can lead to increased inflammation and, if left unchecked, laminitis.
Never use black walnut shavings in stalls or house horses in an area with black walnut trees!
Be Observant
Finally, it is important to know your horse! Be keenly aware of their behavior and be able to notice any changes. Pay attention to any limping, shifting of weight, or heads being lifted too high. These could all be signs of laminitis.
Extra resources
- MadBarn – Founder in Horses
- UC Davis Veterinary Medicine – Laminitis
- AAEP – Laminitis: Prevention and Treatment
- American College of Veterinary Surgeons – Laminitis in Horses
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