Rachel A Nydam
The Laminae And - What Puts the Lame in Laminitis?
All photos and information taken from "The Illustrated Horse's Foot" by Christopher C. Pollitt, "The Essential Hoof Book" by Susan Kauffmann & Christina Cline, and "Distal Limb Pocket Guide" by Jenny Edwards and Paige Poss.
The laminae are an incredibly intricate and fascinating structure that live within the hoof capsule. The image above looks to me as if it could be either wall paper or a fancy abstract art painting. It is actually a microscopic photograph of a healthy horse's laminae. These interlocking strands of material, feather like in appearance but not in substance, lie between the outer hoof wall and the surface of the coffin bone (or P3, or pedal bone).
The folds of stiff tendon-like material that attach to the inside of the outer hoof wall are called the "insensitive laminae" as well as the "epidermal laminae". The insensitive laminae are visible from the bottom of the hoof as what is called the "white line". Beginning with the outer edge of the hoof as seen from the bottom, there is the outer wall or "horn", which may or may not be pigmented (if you have a white or black hoof), then the "white zone", which actually IS white (sometimes called the water line), then the actual "white line", which is really sort of yellow.
The epidermal laminae interlock with the "sensitive laminae" or "dermal laminae" which attach to the outer surface of the coffin bone.
Collagen bundles of connective tissue called the Suspensory Apparatus of the Distal Phalanx (SADP) connect the coffin bone with the dermal laminae.
Connecting the epidermal and dermal laminae to each other is the Basement Membrane, another form of connective tissue. The Basement Membrane holds receptors that direct the growth and function of the laminae. Throughout all these structures run all the necessary veins, arteries and capillaries necessary to provide the hoof with the circulation it needs for optimum health.
Proper circulation is essential for the hoof. There is only ONE major artery for blood delivery to the foot below the fetlock joint. The arterial branches within the foot circle around it and can provide blood flow from either direction. The heart pumps about 70 liters per minute, which at a gallop increases up to 300 liters per minute. Factored out, approximately 225 ml per minute are flowing to the hoof at rest, and up to 712 ml per minute during work. The blood supplies glucose as fuel for growth and sustenance. A single foot will consume 15% of the glucose in the blood, while the whole head only consumes 8%.
As a team, all the laminae together with the SADP serve to suspend the coffin bone within the hoof capsule, and dissipate shock from the hoof's impact with the ground. They protect the bones, ligaments, tendons, and blood vessels from concussion. When the horse takes a step, when the hoof is placed upon the ground, the bone column pushes downward, stretching the laminae, pressing down on the sole, and "vacuuming" blood into the circulatory system of the hoof. When the hoof is picked up, everything is able to bounce back into place. Since there are no muscles in the lower limb, this movement is essential for circulation. Even standing, the horse loads and unloads the feet by shifting his weight even though we don't really see it. Sixty seven percent (67%!) of the vibrations caused by impact are absorbed by the SADP before they reach the bone column. At a gallop, the feet disperse up to 1.7 times the horse's total body weight.
So all this to say, the laminae are VERY important! Any disruption in how it functions has serious consequences! Let's talk about that!
WHAT PUTS THE LAME IN LAMINITIS?
By definition, anything that ends with "itis" means inflammation. Laminitis then means, inflammation of the laminae. This can be mild and chronic, or severe and acute. "Founder" is a term associated with laminitis. Founder is the term used to describe when the coffin bone is no longer in it's normal position within the hoof capsule. So a horse can have laminitis but not founder.
In a nutshell, what happens is that the two interlocking sides of the laminae, the outer (epidermal) and the inner (dermal), let go of one another. Come apart. Separate. The inflammation causes a mechanical dysfunction, and the bone column is no longer supported by the SAPD. Here's what it looks like in microscopic photography. Compare this with my headline image.
As the caption states, this is a severe case. And what happens next is the coffin bone either rotating downward and/or sinking from it's proper place and pointing and falling down towards the sole. Here is a photo of two x-rays, the top of a normal hoof, and the bottom of a horse with laminitis:
You can clearly see the difference in the distances and position of the bones. The laminitic hoof has rotated AND sunk from it's proper position.
And what may happen after that is the tip of the coffin bone penetrating through the sole. Sorry for the graphic photo, but if it will help save a horse in the future:
Hopefully after seeing this, you are asking, can this be prevented?! Yes! Most of the time, YES. Can a horse be saved? Maybe! As the saying goes "an ounce of prevention is worth a pound of cure".
There are a few different ways a horse can become laminitic. Most of them are totally preventable by the diligent care of their humans. Laminitis is typically found in both front feet, though it is possible for it to affect all four.
1. Diet. Excess sugars and starches (non-structural carbohydrates) are not beneficial to any horse, however there are some which are very sensitive. A metabolic imbalance causes some to become insulin resistant. An overload of sugars can tip the good/bad probiotic bacteria balance in the digestive system. This causes a "leaky gut", through which necrotic (dead) bacteria pass through, and "something happens" via the circulatory system to the feet. I put "something happens" in quotes because horse scientists still don't have all the minor details together. It's hard to study! There can be loads of sugars in fresh grass, so horses out to pasture have a higher risk, especially if they are getting added sugar and carbs in their feed rations. Pastures under stress are particularly high in sugars, which is why there is usually an increase in vet calls for laminitis in the spring, when new grass is growing. They can also be higher or lower in sugar depending on the time of day, or after a frost.
2. Sudden overload of sugars and carbs. "My horse got into the grain bin last night", and now he can't walk. The story here is much like number one, but much more acute.
3. Sudden gastrointestinal distress and/or "colic". This may be tied into number 2, but also colic or colitis for various reasons can cause a secondary laminitis event.
4. "Road Founder". Hard work on hard unforgiving ground surfaces, when the horse has not been conditioned to it, can cause a mechanical laminitis. Damage to the blood vessels and laminae can force their breakdown and separation. I'm not saying don't ever trot Fluffy on the pavement. But I might say, don't pull Fluffy out of the pasture for the first time in four months and go trotting down the pavement for 5 miles. And certainly not if Fluffy is barefoot. If Fluffy is barefoot and you want to go trotting down the pavement or gravel, either work him into it gradually, or provide him with some boots. If Fluffy is shod and you want to pound the pavement on a daily basis, I'd suggest some pads and packing to soften the blows. Gravel roads can be equally unforgiving.
5. Supporting limb laminitis. If your horse has sustained an injury in one front leg, the other leg is at a risk for laminitis simply because it is supporting all the weight. Talk to your vet about this possibility.
Let me add to my comments about metabolic or insulin resistant horses. This is somewhat similar to diabetes in humans. There are just some people who really shouldn't be eating a lot of sugar, and none of us needs it. If your horse has what I call a "gutter butt" (meaning if your poured a quart of water on his butt it would only go one way (down his spine)), if he has fatty deposits at his tail head, shoulder pads, and a heavy crest on top of his neck, you should very seriously check his diet. And if you want to know for sure, your vet can check his blood to test for it. There are breeds who are more susceptible, namely Arabs, Morgans, drafts and crosses, and most ponies, but this is not exclusive.
Nutrition is a subject for another blog post, but I'll repeat, stop the sugars and excess carbs (corn, wheat middlings, by products, etc..). Limit pasture time, or turn out with a grazing muzzle. I know, it's sad! But it could save his life. Please consider slow feed hay nets. One to 1 1/2 inch openings. Larger openings are not really slow. It is MUCH better for their metabolism and their state of mind to eat their hay slowly and longer than all at once and then be hungry for hours. You can pull some clumps out of the holes with your fingers to get them started and then they figure it out and hate you less.
Another means of prevention that I will recommend is keeping your horse to a regular schedule of trimming and shoeing. If the toes grow too far beyond the point of breakover, the extra length puts undue stress on the laminae internally, by acting as a lever. Every time a long toed horse takes a step, it is acting as a pry bar internally. Additionally, being out of balance on one side or the other, can cause flares that can cause separation of the laminae. Keeping distortions like this at a minimum is only possible with regular hoof care on a schedule that I will recommend, typically 5 -6 weeks after any major distortions have been brought under control.
Horses by nature are very stoic. They have a very established priorities, and being able to flee from danger and avoid being a predator's lunch takes priority over whether they are feeling a little ouchy in their toes. There may be signs that a horse is in or has been (past tense) in laminitic discomfort or distress, that people miss because the horse does not appear lame. If your farrier tells you that your horses's white line appears stretched, that's a sign. If your horse has pronounced rings at various intervals on the outside of his hoof, or the top edge of his hoof at the center dips down making a subtle "V" shape, those are other signs.
But, if you check on your horse and he is standing like this:
you've got a problem. Oh, and look at the front feet in that photo!
Here's another one:
If your horse is having an emergency like above, call your vet, call your farrier, and get his feet into some buckets with ice, or ice boots, and if you are able, get him onto some foam or thick styrofoam like this:
Duct tape and foam. Garden kneeling pads, any kind of foam you may have, I've even heard of people using flip flops. People kind.
Your vet and farrier will want to see X-rays to know precisely how to go forward with care for your horse. They need to see the degree of rotation and the measurement of any sinking of the coffin bone. Your horse's chances for survival will depend on the diligence of care he receives and how he, as an individual, responds to the appropriate treatment.
If your horse appears mildly lame, or somewhere in between "off" and "not walking", check his feet for heat and a digital pulse. Standing to the side of your horse, hook your first and second fingers around the corner of the pastern towards the heel and if you feel throbbing, he is having an issue. Call your vet.
Many horses make amazing recoveries and return to work with the right kind of care and hoof support via shoes and pads or boots. Some horses may only return to light work or may only be pasture sound. For some euthanasia is the humane choice. It all depends.
The best way is to do all you can to prevent it. I can help!