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By Allison Armstrong Rehnborg
Laminitis, or founder, may be one of the most devastating diagnoses that a horse owner can receive regarding lameness in their horse, but it’s also one of the most mysterious. Thanks to advances in research and decades spent diagnosing, analyzing, and treating the disease, modern large animal veterinarians and equine scientists know quite a bit about laminitis. But there are still aspects of this condition that remain a mystery – starting with its name.
“If you look at the word, ‘laminitis’ means inflammation of the laminae,” explains Steve Adair, DVM, professor of equine surgery at University of Tennessee’s College of Veterinary Medicine. “But we haven’t truly documented that [laminitis] is an inflammatory problem. There are several theories out there. The inflammatory theory is one. And then you have the vascular theory, where you have disturbances in blood flow. There’s also the endocrinology aspect, where you get into horses with insulin resistance and equine metabolic syndrome.”
Regardless of how the damage may be caused, the fact remains that the condition known as laminitis involves a compromise or weakening of the laminae in the equine hoof – which typically results in pain and lameness for the horse. Horses suffering from laminitis often exhibit a short, choppy gait, are reluctant to turn in tight circles, and frequently stand with their front feet “camped out” in front of them as they attempt to alleviate pain by shifting their weight to the hind feet. These symptoms are all due to a breakdown of the laminae, which serve as key supporting structures in the hoof.
In describing the anatomy of the normal hoof, Dr. Adair likens the laminae to a “sling” or hammock, which supports the coffin bone within the hoof capsule and keeps the horse’s natural conformation of bones and hoof wall in line.
“The laminae are almost like Velcro,” Dr. Adair explains. “You have a lot of sheet-like fingers and structures coming off the bone, and corresponding fingers and structures coming off the hoof wall, and those interdigitate, or lock together -- just like when you shuffle a deck of cards.”
In a healthy hoof, those structures between the coffin bone and the hoof wall remain firmly linked, keeping everything in place. But in a laminitic hoof, laminae become compromised and start to weaken, losing their hold on bone and hoof wall.
“Depending on the severity of the compromised laminae, you can get little or no rotation of the coffin bone to complete detachment of the hoof wall from the coffin bone,” Dr. Adair says. “In those cases, the horse walks right out of the hoof.”
Another common mystery surrounding laminitis involves the use of the term “founder.” A common layman’s term for laminitis, “founder” denotes the sinking of a ship – or, in the case of the foundered horse, the sinking or complete rotation of the coffin bone within the hoof as the laminae detach. While some people prefer to use the terms “laminitis”and “founder” interchangeably, others view laminitis as a term for mild cases of the disease and prefer to label severe cases as founder.
Regardless of how the terms are used, it’s the degree of rotation of the coffin bone that really determines the severity of a particular case – and no one knows that better than long-time farrier Dudley Hurst.
“Everyone automatically discusses degree of rotation in cases of laminitis,” says Hurst, Manager of Farrier Services at the Equine Performance Medicine and Rehabilitation Center at the University of Tennessee Veterinary Medical Clinic in Knoxville, Tennessee. “We’re talking about the angle that’s formed from the outside of the hoof wall and the top of the coffin bone. When you think of laminitis and how it affects the hoof, we always qualify statements with, ‘he rotated ten degrees’ or ‘six degrees.’”
Although the biological mechanism that causes the laminae to weaken or die isn’t fully understood, many horse owners – and all veterinarians – know the typical catalysts for laminitis by heart. Retention of the placenta, using black walnut shavings for bedding, excessive concussive stress, and trauma (such as surgery or colic) are all common causes of laminitis. But dietary-related laminitis, or “grass founder,” is probably the most frustrating variant of the disease – not least because of its chronic nature and wild variation in severity.
“Sometimes we get mild, short-lived cases of laminitis,” explains Christine Cocquyt, DVM, equine internist at the Tennessee Equine Hospital in Thompson’s Station, Tennessee. “In those cases, the horses are footsore for a few days, respond really well to anti-inflammatories and rest, and they do really well. In more moderate cases, other horses may respond well to shoeing changes that make them more comfortable. In more severe cases, it seems like there’s nothing you can do to keep that horse comfortable. And those cases can really impair a horse’s future health and ability to have good quality of life.”
Grass founder is most commonly associated with “easy keepers,” those horses that can gain and maintain weight easily and often store large amounts of fat in strange places, such as in the crest of the neck, in front of the sheath or udder area, and around the tail head. These horses can also often be classified as suffering from “equine metabolic syndrome,” or EMS, a condition which encompasses increased fat deposits, insulin resistance, and a predisposition to laminitis. For EMS horses, any sudden excessive intake of sugary, starchy spring grasses can trigger a dangerous chain reaction in the gut, causing a painful bout of dietary-related laminitis.
According to Dr. Rhonda Hoffman, who holds her Ph.D. in equine nutrition from Virginia Tech and currently serves as professor of horse science at Middle Tennessee State University in Murfreesboro, Tennessee, bouts of dietary-related laminitis often begin with an imbalance of good and bad bacteria in the equine gut.
“A normal horse has a cecum and large intestine that are functional,” Dr. Hoffman says. “There’s good bacteria that works in balance to help the horse, and there’s some bacteria that can be harmful in large amounts. The good bacteria works to help the horse digest fibers, like in forages and hay. But if a horse gets too much rich pasture or grain that reaches the cecum, then it promotes more of the bad bacteria, which produces a high amount of acid. That acid damages the lining of the cecum and large colon, the good bacteria begins to die, and the contents of that bacteria are released and absorbed through the damaged intestine. Those endotoxins then enter the bloodstream. Exactly why that endotoxin targets the hoof is the big question no one’s been able to answer, but that toxin goes to the hoof and affects the laminae.”
The overloading of the gut with rich grass – or large quantities of grain, as when a horse breaks into the feed room overnight – is often thought of as the first step in a dietary-related laminitic case, but for horses with EMS, it may just be the latest event in a series of hormone- and insulin-related triggers.
“The more overweight a horse is, the higher risk it has of developing laminitis,” Dr. Hoffman explains. “As a general rule, overweight horses have a slight change in metabolism that makes them more susceptible to laminitis.”
Noticing your horse’s tendencies toward obesity or easy weight gain is usually the first step in preventing an occurrence of laminitis. But it’s easy for excess poundage to start creeping up on a horse, especially during the summer months when it may be turned out on pasture. It’s also easy for horse owners to miss some of the earlier signs of laminitis, which can be subtle at first.
“Nobody wants their horse to be lame,” Dr. Christine Cocquyt, a horse owner herself, admits. “So we make excuses for it. But if your horse is walking gingerly or not wanting to turn or showing any mild signs that their feet are sore, that needs to be addressed. It’s not something to be brushed under the rug until it gets better. Clearly, this year, they have laminitis – but when you dig into the history, that horse may have had mild laminitis in past years, when they just got sore for a couple of days or weeks and then got better. You can certainly have cumulative effects, and getting on top of that during the first episode, rather than the third or fourth, is always better regarding long-term outcome.”
Ultimately, whether your horse has a history of dietary-related laminitis or not, the surest way to diagnose and treat an episode of laminitis is to put your veterinarian on the case.
“You have to have a good relationship with both your veterinarian and your farrier,” Dr. Hoffman says. “In the early stages of laminitis, you’re definitely going to need help from the vet to figure things out.”
While some conditions in the horse can be remedied fairly quickly, laminitis isn’t one of those get-fixed-fast problems. Especially in cases of grass founder, painful and damaging episodes can occur again and again, requiring a long-term commitment from the owner to manage and monitor the horse’s diet and condition.
“Once you have a horse that has had changes in the laminae, you always have to be pretty diligent about preventing the triggers that may inflict that,” Dr. Cocquyt says. “If it’s a metabolic problem, managing the diet and environment of the horse is important. If there are changes in the structure of the foot and there’s rotation in the coffin bone, you’ve got to manage the pressures on the laminae. I definitely think you have to be pretty astute about that horse’s condition, know about it, and know what may have been a predisposing cause so that you can continually work to prevent any changes and detect early signs of another episode.”
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