NOTE! This article is on Laminitis. Laminitis is often confused with Founder. Laminitis and Founder are two different conditions, not synonyms. We recommend reading our full series on laminitis before moving on to learning about founder.
Defining Laminitis
The word laminitis means “inflammation of the laminae”, and it is a systematic condition that affects the whole horse, not just its feet.
Laminitis can be incredibly painful and can become life-threatening if not promptly addressed.
While laminitis affects many systems within the horse’s body, the hooves are most severely impacted by this condition.
Inside the Horse’s Hoof
To understand laminitis, we need to know what’s inside a horse’s hoof. Take a look at the drawing below and familiarize yourself with the structures of the horse’s hoof that are involved in laminitis.
This will help you better understand the rest of the information contained in this article.
Coffin Bone:
The coffin bone is the last bone in the horse’s leg, and the one that is closest to the ground.
Laminae:
Think of the laminae as velcro: one side of the velcro is attached to the coffin bone. We call it the “sensitive laminae”.
The other side of the velcro is attached to the hoof wall. We call it the “insensitive laminae”.
These two layers interlock (just like velcro) and keep the hoof wall and the coffin bone joined together.
Hoof Wall:
The hoof wall is a thick layer of dry, hard, and non-sensitive cells.
We call these cells “keratinized” or “cornified” cells, and they are the same type of cells that make up our fingernails and hair.
The purpose of the hoof wall is to protect the sensitive structures contained inside.
White Line:
The white line is a continuation of the laminae. We discussed how the purpose of the laminae is to keep the hoof wall and the coffin bone attached to one another: as the hoof wall grows down toward the ground, the “old” laminae grow past the bottom edge of the coffin bone.
Once the laminae grow past the bottom edge of the coffin bone, we begin calling it the “white line” This is now the point of attachment between the hoof wall and the horse’s sole.
What happens during laminitis
When a horse gets laminitis, the laminae start to get inflamed. Inflammation means that the body’s tissues become swollen and sore, often due to things like injury, illness, or even eating too much of the wrong food. Read our article “Laminitis 102, What Causes Laminitis” for a more in-depth dive on this topic.
When the laminae get inflamed, they don’t work as well. This is a problem because, as we said, the laminae are what hold the bones inside the horse’s hoof in place.
Here’s what happens next:
1. Inflammation
In a healthy foot, the sensitive and insensitive laminae are tightly connected.
When laminitis starts, the laminae become inflamed, and this is when the horses enters the “acute phase” of laminitis.
2. Swelling
The inflamed laminae become swollen. This leads to a build-up of excess pressure inside the hoof, as there is no physical space to accommodate the increased size of the swollen laminae.
3. Pain and Lameness
The pain caused by this swelling leads to varying degrees of lameness; many horses will be in so much pain that they will be reluctant to move, may stand in unusual ways, or may even lay down and refuse to stand up.
4. The Bond Weakens
As the swelling continues, the bond between the hoof wall and the bone inside begins to weaken.
The laminae are no longer as strong as they should be, and they can’t hold the bone and hoof wall together properly.
When you look at the bottom of the hoof of a horse that had a laminitic episode in the recent past, you are very likely to see a stretched white line: this is a sign that the horse has gone through a laminitic bout that weakened the bond between sensitive and insensitive laminae.
What is the horse feeling?
Have you ever done one of the following?
Slam your finger in a car door or house door
Hit your finger with a heavy object such as a hammer
Drop a heavy object such as a dumbbell on your toe
Stub your toe on a hard surface
If you have, you may also have experienced a “bruise” underneath your nail.
The blood that pools underneath the nailbed creates a similar kind of pressure that the swollen laminae create in the horse’s foot.
If you have ever experienced a bruised nail (a subungal hematoma), you have experienced a fraction of the pain experienced by a laminatic horse.
When you damage your nail, you will likely choose to be careful with that finger and not use it in any activity that may cause pain.
A horse has no choice but to stand on its feet and experience that pain with every step.
What does it look like?
From the owner’s point of view, laminitis should be treated as a serious emergency.
1.Developmental phase
During the developmental phase of laminitis, there are no noticeable symptoms. This phase lasts 30 to 40 hours.
2. Acute Laminitis
The “acute phase” of laminitis will be a sudden onset of pain and lameness.
At this stage, the horse is experiencing extreme pain: he will be reluctant to move, and may assume what we call a “laminitic stance”.
The “laminitic stance” is a result of the horse attempting to shift it’s weight onto the hind end and away from the front feet.
If you see your horse standing in this position, you must call your veterinarian immediately.
3. Damage to the internal structures
During the acute phase of laminitis, the fibers that hold the coffin bone and the hoof wall together are damaged.
There is no way for veterinarians to quantify the level of damage done to these structures, (how many fibers were damaged, how long the episode will last, etc,.) so the protocol in laminitic cases is to treat them all by assuming a “worse case scenario” outcome.
All laminitic horses are in fact treated as if they had “foundered”. As we already mentioned, laminitis and founder are not one and the same: founder is the worst possible outcome of an episode of laminitis. It is a potential consequence of laminitis.
For now, all you need to know is this: not all laminitic horses have/will founder, but all foundered horses had laminitis.
We will dive deeper into founder later in this series. Read Laminitis 102 next!
Self Assessment Quiz
Multiple Choice Questions
What is the primary function of the laminae inside a horse’s hoof?
a) To provide extra cushioning for the hoof
b) To hold the hoof wall and the coffin bone together
c) To increase blood circulation in the hoof
d) To create keratinized cells for hoof growth
What causes the initial pain and discomfort in a horse suffering from laminitis?
a) A bacterial infection in the hoof
b) Excess swelling and pressure inside the hoof
c) A lack of blood flow to the hoof
d) The horse standing on hard surfaces too long
What is the “white line” in a horse’s hoof?
a) The area where the sole meets the hoof wall
b) The area that produces the hoof wall
c) A natural crack in the hoof that absorbs shock
d) A line created by the separation of the hoof wall during laminitis
Why do horses with acute laminitis often stand in a “laminitic stance”?
a) They are trying to cool their hooves by lifting them off the ground
b) They are attempting to shift weight off their front feet
c) They are attempting to load their weight onto their front feet
d) They are stretching their tendons to improve circulation
True or False
___ Laminitis is only a foot condition and does not affect the rest of the horse’s body.
___ Founder and laminitis are the same condition and can be used interchangeably.
___ The developmental phase of laminitis lasts 30 to 40 hours and does not show noticeable symptoms.
___ All cases of laminitis should be treated as if they could result in founder.
Short Answer Questions
Describe how the laminae function like Velcro inside a horse’s hoof and why this is important.
Explain why laminitis is considered a medical emergency and what steps an owner should take when noticing signs of acute laminitis.
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