In terms of it's potential for long, drawn-out agony, laminitis is the worst malady that can strike a horse. Unless somehow the owner and vet manage to catch and reverse the process of inflammation and deterioration in the laminae -- the tissues that connect the coffin bone, or third phalanx (PIII), to the inside of the hoof wall -- early enough, the coffin bone sinks within the hoof capsule, turning laminitis into founder.
Once that happens, in some way even a horse with acute colic is luckier. But a severely foundered horse, whose coffin bone rotates out of alignment and descends, perhaps far enough that it goes through the sole, may go on and on in severe pain until his owner decides that putting the horse down is the only decent thing to do.
Even if the acute problem eventually subsides, the horse is likely to be left with a considerable residue of chronic discomfort. He may habitually stand rocked back to minimize the amount of weight he puts on sore front feet; his bones may be so misaligned that every step he takes puts some degree of unnatural stress on them; and periodically he may feel even more pain when inflammation flares up in the old trouble spots.
Within the last twenty years, however, the chances of catching laminitic deterioration in time and turning the condition around before things get that bad have greatly improved -- thanks to advances in veterinary research and in my own field of farriery, and thanks also to a growing understanding and cooperation between the two fields. We still don't fix every one of these horses, but we are fixing a lot of them that we wouldn't have twenty years ago.
In this article I'm going to tell you about some of the changes in treating, in technology, and in the thinking behind both that have enabled us to do so much better than we used to (though still not as well as we'd like). I'll also be talking about how, if laminitis strikes your horse, you can take advantage of these better treatment methods and help them work to best effect.
Heart-bar shoes and hoof-wall resections, two of the advances I mentioned earlier, are part of the reason for our improving record with victims of laminitis, and I'll be telling you about them. But besides all the insights and improvements that veterinary science and farriery have come up with, there are two other crucial factors that affect a horse's chances of surviving and returning to some degree of soundness. One is the horse himself -- how much he's suffered, how much infection is present in his feet and elsewhere in his body, and how much of a survivor he is -- how much he's willing to keep fighting. The other, as you'll see in the comeback program I sketch out, is a partnership of owner, farrier, and veterinarian committing themselves to work together to give the horse the best chance they can.
The commitment is demanding, as I try to make clear to anyone who calls in to work on a laminitic horse: It's expensive, it may need to go on for months or years--for the rest of the horse's life in some cases -- and it carries no guarantee of a positive outcome. But in the horses I've worked with that have come back, it has been a major reason for our success.
Before going into the "how" technicalities of working with a foundered horse, I want to tell you a little about the "why" -- because besides being the worst malady that can befall a horse, laminitis has long been one of the least understood.
For hundreds of years, horsemen understandably saw laminitis as a problem of the feet; when a horse foundered, they concentrated on fixing his feet. Along the way, they came up with a number of treatments--hoof casts, nailing the shoes on backward, stretching down the tendons, and so forth -- that became accepted (and were written down in books, some dating back to the 1850's or before) as "standard" because the produced relief in some cases, although they did nothing (or even did damage) in others.
Those some treatments got carried on to the next generation of books and the next. Even today some horsemen and farriers -- and some veterinarians who don't see many horses, and who don't manage to attend many continuing-education courses or come to national conventions -- regard them as appropriate for any foundered horse.
Despite such lingering misunderstanding and misinformation, however, most veterinarians, farriers, and horsemen have come to understand that in laminitis, the feet are normally the secondary problem. While some cases of are caused mechanically, by long work on hard surfaces or by trimming and shoeing that put excessive stress to the feet themselves, others -- those with the greater potential for threatening feet and life -- result from some internal problem that is causing toxic substances called endotoxins to collect in and interfere with blood supply to laminae. In these cases, until we correct that "something", we can't have a hope of correcting the laminitis.
The breakthroughs we've achieved in our understanding of laminitis have come as we've become increasingly able to observe what is going on inside the horse. For example, horsemen long thought (and every book on equine physiology used to say) that the frog pumps blood through the foot. The first researchers who said that it didn't, and that it was actually more of an arch support than anything else, nearly got run out of town. (As the late Louis L'Amour, the Western novelist, once pointed out, "Ideas are welcome as long as they do not contradict theories on which scholarly reputations have been erected.") This revised view of the frog's role gained acceptance only when researchers were able to examine blood circulation through the foot by means of scintigraphy -- visually following the progress of a small injected radioactive substance through the vascular system of the foot.
Like veterinary science, farriery has been and is still learning and revising old ideas about laminitis. The heart-bar shoe (its name comes from its shape -- a V-shaped piece of stock extends from the heels in along the frog to a point about three eighths of an inch short of the apex) has been around for years; the earliest I know of is in a book published in the 1820's, where if was called a "veterinary frog-support plate." Still, there was terrific resistance when we first started using it on laminitic horses. Now, though, there are veterinarians and farriers -- a couple on the East Coast, two or three in the Southeast, two or three in Texas, three or four on the West Coast, as well as some in Canada, Mexico, England, Scotland, and Australia (where some of the best recent work on understanding the vascular system on the foot has been done) -- who have studied it and who have had really good results using heart-bar shoes on hundreds of foundered horses. The number of successes is important because (as all the recent brouhaha about cool-temperature nuclear fusion has reminded us) research is no good unless the results can be reproduced. Enough different veterinarian-farrier teams have had success in enough cases that we believe we can say we have a standard method for working with a laminitic horse.
I'll show you how that method works, including your role as owner, for three hypothetical horses: The fellow who got into the grain bin last night and whose problems haven't progressed beyond simple laminitis; the foundered horse, in whom the coffin bone has begun to tear away from the laminae and descend; and the horse in chronic founder, whose disease is no longer active (except, perhaps, for an occasional bout of inflammation) but who's living with damaged feet. In the first two, as you'll see, our aims are threefold: to stabilize the coffin bone and prevent it from descending any farther than it already has, to relieve the pain caused by inflammation and the swelling that typically accompanies it, and to prevent the infection that might set in if problem sites were not found and treated. In the third, the deterioration is basically done; our focus is on making the horse comfortable.
(Before we go on, however, let me point out that while most veterinarians and farriers are aware of this treatment method today, not all of them have had the opportunity to work with it. And as Dr. Jim Coffman at Kansas State University once said, "Don't just draw a heart-bar shoe on a napkin, hand the napkin to your farrier, and ask him to go put a hear-bar shoe on a horse -- you'll be sorry if you do." If you have a horse with severe laminitis and your own veterinarian or farrier hasn't worked with the techniques I'm talking about, you may want to call the nearest veterinary school with a large-animal clinic, such as Texas A & M or the University of Pennsylvania's New Bolton center, for a reference. As the health consumer, you have a right and responsibility to ask questions, and if the answers you hear leave you uneasy -- if, for example, someone proposes putting a hoof cast on your horse who's newly foundered -- you should look for a second opinion.)
The evidence is clear when you arrive at the barn: Your horse is out of his stall and in the feed room, the grain-bin lid has been nosed open, and the bits of grain scattered about the floor and sticking to his muzzle seem to outnumber the few left in the open feed sack. But he's having little joy from his night of stolen delights -- he's extremely stiff, glued to the ground, and his pulse is pounding. He may seem to be trying to keep his weight back toward the rear, because his front feet (which normally carry about sixty percent of a horse's weight) feel especially tender. His insides are in an uproar, with the carbohydrate overload he's taken in working all sorts of havoc on the natural chemistry of his gut (although he probably won't be running a fever of showing signs of diarrhea or constipation).
Your first step, of course, should be a call to the veterinarian. If he arrives quickly enough, he may be able to reverse the problem with medication while it is still just a chemical one. While you're waiting for the vet to arrive, though, you can make the horse more comfortable if you apply a temporary frog support. At this point only a small percentage of laminae (if any) are likely to be damaged; if you support the frog from below now, you may prevent further tearing.
The material I recommend for this kind of first aid is indoor-outdoor carpeting. Cut it in triangular pieces the shape and size of the frog (with a little extra at the base to go up over the heels), stack enough pieces on the frog that the pile projects a quarter to three eighths of an inch beyond the bearing surface of the foot, and tape the support up around the hoof. If you don't happen to have indoor-outdoor carpeting, you can tape a roll of gauze under the frog instead; just don't use anything hard or unyielding, such as plywood, which could create additional problems by applying too much pressure. (You can buy temporary frog-support pads, but they're expensive, they're not reusable on any other horse, and I don't think they do any better job than indoor-outdoor carpet does.)
Once the veterinarian arrives, he'll administer medication to counteract the internal effects of your horse's binge; he'll instruct you to call him immediately if you see any recurring signs of discomfort. (He may warn you to be particularly watchful fifteen to thirty days after the original incident, which is the time abscesses typically take to form if a foot has any dead tissue entrapped within it.)
Unless the x-rays show a change form normal bone position -- which they probably won't if this is in fact a simple case of carbohydrate overload and you've caught it early enough -- the vet probably won't suggest having the farrier for anything particular for the foot. If there is change, he may confer with the farrier about putting heart-bar shoes (which I'll go into in more detail below, under "The Long Haul" -- because a long haul is what you'll be facing).
If you do detect a return of soreness, it's time to call the vet again. He'll open and drain any abscesses he finds (more about this below, too), and he may run blood counts to make sure no previously unsuspected infection is complicating your horse's recovery.
While a simple carbohydrate overload may not turn into founder if it's caught early enough, I regard every case of laminitis as an emergency -- because the crossover line is a very thin one, and a horse who's gone into founder is a horse in real trouble. This is where all the time and expense and potential heartbreak come in -- not so much in the initial day or two, but in the ninety to 120 days (or more) of intensive care the horse is to need to survive and come back. And this is where I try to do a lot of work up front, making people aware of the kind of commitment they're going to have to make -- in terms of time, money, and cooperation with the vet and farrier -- to have a chance of bringing back the horse to some degree of soundness.
Many of the foundered horses I get called in on are those in which the condition had progressed so far -- for any of a number of reasons, including inappropriate treatment -- that they have no hoof left at all; they're lying in the stall, covered with decubitus ulcers (bed-sores). These horses are the ones that have the least chance of being saved. I spend a lot of time with the owner of a horse like this (and with his regular veterinarian and farrier), making sure he understands that this is the horse's last chance, that it's going to expensive -- at least $12 or $15 a day in bandaging costs alone if the horse requires a hoof-wall resection, not to mention all the rest of the fees -- and that there's no guarantee of success, no matter how hard we try. All I can do is promise him that the vet and I will give it 110 percent, and that if the owner will work along with us we'll see where we are after, say, twenty days or so.
That extreme picture isn't where things start off, of course, so let's begin talking about founder at the beginning -- with a horse whose treatment begins fairly early but who has more go wrong internally than did our grain-bin raider.
A horse whose coffin bone has started tearing away from the hoof wall needs both medical and mechanical attention: from the vet, who works on identifying and correcting the underlying condition that's creating laminitis, and from the farrier, who concentrates on stabilizing the bone and keeping it from dropping and farther. If that bone is stabilized early, when maybe only fifteen or twenty percent of the laminae have been damaged, the rest of them are less subject to fatigue and tearing, and less likely to swell and shut off circulation to the rest of the foot (a major cause of tissue death or necrosis, which can actually cause the hoof to sough off).
One reason for regarding every case of laminitis as an emergency is the fact that there's no way to tell how quickly a horse may founder. I've known cases where an unsupported third phalanx has detached completely and come through through the sole, without even rotating (a condition called "sinker," which I'll tell you more about shortly), in as little as eight hours. That's why I recommend applying a temporary frog support while you're waiting for the vet to look at any horse whose feet have come up sore, and why I put heart-bar shoes on any horse who comes to me with laminitis as soon as I see the x-rays and know how much support he needs. (Given the amount of work I've done in this area and the relationship I have with the vets I work with, most of them simply give me the x-rays and say, "Burney, go and put a set of heart-bars on that horse." If either the vet or the farrier isn't so experienced in this area, the two of them would want to do more conferring beforehand.)
Each heart-bar shoe has to be built individually -- even different feeton the same horse are likely to show different degrees of the problem. If a radiograph shows that the bone is still normally positioned, even though there is some swelling of the laminae, I elevate the heart-bar portion of the shoe so that it puts no more than 1.5 to 2 millimeters (about the height of a quarter and a dime to two quarters) of support under the frog -- I don't want to run the risk of cutting off circulation and causing pressure necrosis. For the same reason, I'm careful not to let the shoe touch the sole.
The heart-bar shoe I put on a horse whose hoof wall is in tact and whose laminitis is in an early stage is made out of half-round stock with a toe turned up in front like a sled runner. That moves the fulcrum point for the foot back to where it's nearly right under the point of the third phalanx, so that when the horse moves forward, he needs less energy -- and puts less pull on the bone -- to break the foot over.
Normally the horse walks off more comfortably as soon as he's had heart-bar shoes put on. If we're lucky, that may be the end of the problem, although the owner should keep keep an eye out for soreness, and the heart-bars should be reset (and the shoes replaced if changing foot shape requires it) every thirty days for the next six months or so. Their horse should also be given plenty of chance to exercise, since exercise stimulates circulation and so brings the tissues in his feet the oxygen and other nutrients they need for repair.
I like to have the horse radiographed when I reshoe at the end of the first thirty days. I want to see whether there's been any change in the position of the bone and how I may need to change the setting on the support bar. If I see no change then, and if his condition progresses smoothly, I may not ask for new x-rays when I reshoe at the end of sixty days -- but I will want them again at the end of the third month to see if he's actually lost any bone (a problem that takes ninety to 120 days to show up). If he hasn't, his chances of coming back athletically sound are good.
Six months after the initial shoeing, I may try a horse out with half-round shoes without the rolled toe, or even normal shoes -- and let him go back to them permanently if he walks off comfortably. If he doesn't, though, he may always need the support of a heart-bar shoe -- just as some people always need arch supports in their shoes.
Unfortunately, with a lot of horses, things don't go as smoothly as I've just described. There are many problems that can appear along the way; the sooner they're detected and corrected, the better the horse's chances.
The same problem may show up in the other foot at a later date; if so, the vet and farrier will probably follow the same procedure.
In some cases, simply opening a small hole is not enough to relieve pressure on the laminae and clear up an abscess. The horse may need to have an anterior hoof-wall resection -- removal of part of the front hoof wall, which not only gives swollen tissue room to expand without shutting off blood supply to the laminar corium (the "nail bed") and the bone but also allows access to any necrotic tissue trapped between the coffin bone and the hoof wall. (Systemic antibiotics won't help the problem here. The whole reason you have a problem is that swelling has shut off blood flow -- so a systemic medication just isn't going to get where it needs to go.)
The hoof-wall resection (again, something performed by a qualified farrier under a vet's guidance) is a serious procedure, involving a convalescence of ninety days to a year. During the first sixty to ninety days, the horse will need daily soaking and bandaging of the foot, regular exercise, diet supplementation, visits from the farrier to keep the hoof trimmed appropriately as well as to reset the shoes, and (less frequently) visits from the vet. The owners role in bringing the horse through this procedure is critical; if he doesn't follow the advice of the vet and farrier, and follow up on all the tasks they assign him, everybody's efforts are wasted.
A correctly performed hoof-wall resection is basically bloodless and painless -- it's not surgery, but more like the removal of a fingernail. (It may not look bloodless at first if, as happens in a lot of cases, there is a hematoma -- a pool of accumulated blood -- trapped between the coffin bone and the hoof wall; but once that material runs out, there should be no bleeding to speak of.) Because it is a painless procedure, and because the vet and farrier need to see whether if relieves the horse's basic discomfort, no local anesthetic should be used.
Once the hoof-wall resection is completed, the horse needs frog support so that he can begin the healing process with his hoof wall and coffin bone properly aligned. If the foot is not too painful, and if the horse has sufficient hoof wall left, I normally nail on a heart-bar shoe; if he's really sore, though, I use a glue-on shoe instead (sort of a space age spin off, and a real blessing for horses in this condition). Most glue-on shoes start out as a piece of strong polyethylene plastic, eight or ten inches square. I trace the horse's foot on the pad, then use a jigsaw or band saw to cut out the basic shape and add any configuration I need for the center, like a heart-bar, adding pieces to thicken the heart-bar insert until I have the amount of support I want. Then I weld plastic tabs to the shoe and glue them to the foot. (Another option, particularly for a horse whose foot needs more protection than the glue-on shoe alone can provide, is a glue-on adaptor rim pad that can be riveted to the bottom of a steel shoe; tabs are then welded to the pad and glued to the hoof.)
After a hoof-wall resection, the area needs to be kept bandaged until the hoof wall has regrown. I like to use Elastikon or Vetrap for the bandaging material and cover the sole with several thicknesses of duct tape to keep the bandage from wearing through quite so fast. The bandage itself simply covers the foot, much the way an Easyboot would (but don't consider using an Easyboot instead of a bandage -- it can rub the horse's heels raw if it stays on for any length of time).
As long as there is any drainage in the area, a good topical dressing to use under the bandage is sugardine: a mixture of betadine and table sugar, and something that veterinary medicine had borrowed from human medicine. (The sugar is very compatible with new tissue, not harsh and drying like some of the things we used to apply, and it draws fluids, so it promotes drainage.) Additionally, for the first ninety days or so, it's wise to keep a thick line of ichthammol around the coronary band -- for two reasons: First, the ichthammol is a drawing agent, which will draw to a head any abscesses that can't be drained through the bottom of the foot. Second, the ointment keeps the top of the hoof capsule soft and pliable, allowing maximum blood circulation to the coronary band, which is where new hoof starts to grow.
Soaking or turbulating the foot twice a day, for ten to fifteen minutes at a time -- in hot water and betadine one time, hot water and Epsom salts the next -- will help bring any lurking abscesses to a head; it also increases circulation, and it just seems to make the horse feel better. Once the foot has stopped draining (which means you no longer run the risk of trapping inside it any material that ought to come out), you can change topical medications from sugardine to merthiolate, which speeds up the process of keratinization -- turning the new tissue to horn.
Exercise, like soaking, helps the healing process by increasing circulation and encouraging drainage. In my barn, for example, as soon as a recuperating horse's hoof wall and bone are stabilized, he goes outside and stays out as long as the weather's good; he comes in (to a box stall deeply bedded in clean straw -- which is less abrasive and less likely to ball up than shavings -- or, better yet, shredded newspaper) only if the weather's bad. If you don't have that option, you should still get your horse out of his stall and walk him at least six or seven times a day, for for five or ten minutes at a time, so that he gets a total of about an hour's exercise but gets it in small increments. (Don't hang him on a hot-walker for an hour straight -- you'll do him no good at all. Giving him short periods of work over a whole day comes much closer to what nature intended).
One element of promoting hoof growth is diet -- specifically, supplementing the regular diet with methionine and biotin. Methionine is an amino acid that's essential for hoof development, and biotin seems to act as a catalyst to methionine. Most horses don't like the taste of methionine and refuse to eat it by itself, but there are alfalfa-based methionine-biotin supplements, such as Farrier Formula or Nutri-Tone, that they find much more palatable. (Don't simply feed a supplement that's high in all amino acids; what your horse needs if he's had a hoof-wall resection is something with very high methionine levels to stimulate his hoof growth).
Reshoeing a horse that's had a hoof-wall resection presents special problems. His feet feet are likely to change shape quite a bit -- the heel, which hasn't undergone the circulation squeeze that the toe has, has been growing as much as four times faster and may have started to bend forward under the foot. The farrier needs to trim the foot regularly to keep it as close to its original shape as possible, and perhaps to back up the shoe each time he resets it.
Following a resection, the horse may be a little sore at first because the repositioning of his coffin bone puts a pull on his deep flexor tendon. Muscle soreness normally decreases as he walks more; if he continues to be sore, however, especially if he's still rocking back off his front feet when he stands, you can safely figure that you're seeing foot soreness -- and that he's still got some inflammation. Any of three things could be causing this problem: The preexisting condition that caused the laminitis in the first place may still be active, the feet may still be harboring some necrotic tissue not found in the resection, or the laminae may have sealed up before all the serum from an abscess drained.
The vet or farrier will have to attend to the horse in either of the first two cases, but in the third you may be able to correct things on your own -- so you'll want to see what you can do first. You must get the horse moving briskly (if he's reluctant, have somebody snap a towel at his hindquarters), and keep him going for several minutes. If the problem is trapped serum, there's an excellent chance that this will open up the laminae enough to get it seeping again -- and the horse will immediately move more easily. Then you can go back to your routine of soaking and sugardine until you're certain you've gotten all the fluids out.
If exercise doesn't produce results, however, your next step should be notifying the vet to come out and reassess the situation. Depending on what he finds, he may decide to reopen the sole or even (though more rarely) to do another hoof-wall resection and clean out the problem area.
Once in a while a horse goes into endotoxic shock so sever that it disrupts circulation to the laminae entirely. They just die and let go so fast that the bone doesn't rotate; it simply sinks straight down -- through the sole of the foot. This is the condition called "Sinker".
This kind of horse doesn't rock back on on his feet like a foundered horse; he stands square, but he's very reluctant to move -- so he may be diagnosed as having Monday-morning sickness of myositis. One way to detect that the condition is actually sinker, however, is to run your finger down the horse's leg; if it comes to the coronary band and stops there, and you find there's a distinct depression behind the top of the hoof capsule all the way around the foot -- not just in front -- you're looking at a sinker. The horse isn't in the kind of pain normal laminitis creates -- but because there's nothing holding his feet together, he'll walk out of his hoofs in thirty days if he's not treated.
A sinker should be treated with immediate application of a heart-bar shoe (if the quarters and heel of his hoof are intact) or a glue-on heart-bar device, with a rim pad as well if more height is needed for the prolapsed bone to clear the ground. Then he should undergo a hoof-wall resection. As long as he still has circulation to the coronary plexus (the "circle" of the hoof -- just above it's top, where horn growth begins) and the circumflex artery and vein, which supply the face of the coffin bone and are one of the principal routes of blood to and from the foot, there's a chance that his foot can be saved and his hoof can grow back. Time is of the essence in this kind of case. The chances grow dimmer if circulation here had been impaired, dimmer still if the horse had begun to lose bone.
At his worst, the chronically foundered horse is the fellow you see in the books: the one with the upturned toes and the feet the always hurt to some degree. Depending on how much discomfort he feels, his radiographs may show a severely deformed or remodeled coffin bone, possibly with much of its distal (lower) end gone, way out of alignment with the two bones immediately above it (the first and second phalanx) -- which means that the deep flexor tendon is also deformed. His hoof wall may look dished, the white line may be distorted and as much as half and inch wide, and he may have "seedy toe" -- a big wedge of old laminae trapped behind the hoof wall adding to his pain. A horse with less severe pain may also have seedy toe; on x-rays, the the end of his coffin bone will probably look rough -- evidence of pedal osteitis (inflammation of the bottom of the bone).
A horse with chronic founder is like somebody who's survived polio and is living with the aftereffects. He's not in danger of dying; but depending on the damage he's sustained, he can be pretty miserable. What the vet-farrier-owner team can do for him is provide constant care to make him as comfortable as possible. Anything that gets his foot up off the ground is likely to provide him some relief (he's the one kind of horse who may feel better if somebody nails his shoe on backward). Fixing his foot means doing as much as possible to return it to normal alignment -- rasping his toe back and backing up the foot with a heart-bar shoe to give support under the frog. If the deep flexor tendon has been deformed, he may need his check ligament or even the deep flexor tendon itself cut to relieve the tension on it -- decisions in which the owner must be an active and understanding participant.
A horse with seedy toe severe enough to make him lame may need nothing more than to have his toe rasped back and and a heart-bar shoe fitted to support and help realign his foot. In a few cases the vet or farrier may need to so a resection to get all the laminar wedge -- but the horse probably won't need bandaging; in his case, what's being removed is old dead tissue (a lot like a corn in a human being).
With care, even a horse with severe chronic founder can be brought back to being pasture-sound, or even riding sound in a few cases; a horse with a milder case, though, may do yet better. In either case, though, the need for care never stops. If an owner decides after a year or two that his horse has had enough special pampering, so he stops having the feet trimmed and the shoes reset regularly, he's very soon going to have himself a lame, sorry horse.
In most cases, a horse's laminae begin to deteriorate and die because something has made his internal chemistry go haywire, upsetting the delicate balance that normally allows dozens of different bacteria to coexist peacefully and productively within him. The "something" may be a uterine or lymphatic infection, an infection from a puncture wound, an abscess, a hormonal imbalance, kidney failure, pancreatic malfunction, allergic reaction, gastroenteritis, carbohydrate overload (the aftermath of the classic grain-bin break-in), or perhaps some cause science hasn't yet linked with endotoxemia. Whatever the cause, the results are disruption and destruction.
When a horse breaks into the grain bin, for example, lactobacillus bacteria (which thrive on carbohydrates, and which produce lactic acid) in his gut rapidly begin multiplying. The proliferating lactobacilli increase the acidity of the gut, which heightens the activity of a second acid-producing bacterial form, streptococcus. The resulting highly acid environment wipes out a whole group of other bacteria; as these organisms die, their disintegrating cell walls release endotoxins -- internally produced poisons -- which erode the lining of the intestine and so escape into the bloodstream.
The horse's body reacts defensively to the rise of endotoxin and lactic-acid levels by releasing other chemicals, including prostoglandins -- unfortunately, in such high levels that they create damage of their own, such as constricting the smaller blood vessels and closing down some normal circulatory routes. That can set off one or more additional problems, including complete circulatory collapse (leading to shock and death), colic and all it's attendant complications and dangers, and laminitis.
The laminae are vulnerable to endotoxic damage because the blood vessels that bring oxygen and nutrients to them are so fine that a very little constriction is enough to close them down. When that happens, the laminae become damaged and die in short order. As they do, the horse's coffin bone begins to break free from them; depending on how quickly and completely that happens, the bone may either rotate out of normal alignment and gradually begin descending toward the sole of his foot (founder) or may simply drop straight down (sinker -- a condition in which all of the laminae die within a very short time, before any rotation can occur).
In the early stages, laminae being deprived of circulation become inflamed and swollen, causing pain under the hoof wall that is pinching them in. Later -- normally anywhere from two to four weeks after the problem begins -- abscesses formed around the dead laminar tissue may create additional pain, especially if the fluid-filled abscess is pressing against both the hoof wall and the wedge of dead corium. And the unsupported bone itself, out of alignment and pressing down on the sole from inside, is another source of pain.
A horse who survives his initial bout with endotoxic damage isn't necessarily out of the woods. If infection sets in (a danger greatest where the bone is actually exposed, or where an abscess remains undetected long enough that it turns purulent), there is danger of the bone itself becoming infected. If severe bone infection (osteomyelitis) sets in, the only way to save the horse may be to curette (scrape) the bone to remove dead or infected areas, or even to amputate the leg -- an option few veterinarians would recommend.
© Burney Chapman
Posted here with the permission of the author
first published in The Blood Horse Magazine