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Laminitis: A major and Unsolved Problem for Horses
W.A. Moyer, DVM
Laminitis (often called founder) is a unique disease, which commonly affects horses, ponies, donkeys and mules. It has been diagnosed in zebras and some cloven-hooved animals. It has been recognized as a major problem in the horse world for centuries. It is a reasonably frequent cause of lameness in the less severely affected as well as a legitimate reason for humane euthanasia in the more severely affected. The horse insurance industry recognizes it as one of the most common reasons for an insurance claim. Yet the disease, for all its importance, history, research and concern, remains an unsolved dilemma.
The word laminitis means inflammation (thus the suffix–itis) of the laminae. Laminae are the soft tissue structures that exist between the hoof wall and the underlying coffin bone (or 3rd phalanx). Think of the laminae and lamellar structures like Velcro, attaching and suspending the coffin bone within the hoof capsule. Consider the hoof wall to be like a finger or toenail, the laminae to be the nail bed (the soft and very sensitive tissue under the nail) and the coffin bone to be the very small bone at the tip of a finger or toe. Obviously, the similarity ends with regard to function and load.
Most recently, based on previous work done in Australia, another definition for laminitis has been offered as such: a failure of the attachment between the 3rd phalanx and the inner aspect of the hoof wall. One of the many dilemmas in this complex disease is understanding how this critical attachment is damaged and/or destroyed.
Failure of the lamellar attachment results in loss of the suspension of the coffin bone within the hoof capsule. Thus the coffin bone descends (rotates, sinks or both) toward the bearing surface. The process results in shearing and tearing of arteries and veins, in which case living tissue dies in the absence of oxygen-rich blood flow. The tissues, which once united the structures, are sheared and crushed, with the end result being pain and lameness. Disagreement between scientists and investigators exists with regard to what destroys the attachment. Conventional thinking for years was that of a vascular disorder, that is, something caused the vessels to constrict and thus start the cascade of events. More recent work suggests primary damage (toxic to origin?) to the attachment via loss of the chemical and molecular bonding followed by physical damage to the associated vessels. We do know that a multitude of events can set up this event.
We also know that just about any primary organ or organ system damage has been known to initiate laminitis. This would include problems involving the gastrointestinal, respiratory, reproductive, renal (kidney), endocrine (hormonal such as Cushing’s Syndrome), musculoskeletal, integumentary (skin) and immune systems. Independent toxic events are known to cause this (for example, black walnut shavings). This can also involve toxins produced by bacteria such as Salmonella. Various metabolic disorders are classic examples: grain overload (grain founder) and the ingestion of certain grasses at certain phases of growth (grass founder). Various drugs have been implicated (steroids) but not proven. Based on observational studies, stress (which is difficult to define) has been suggested to initiate laminitis (for example, horses exposed to heavy showing schedules with great shipping distances, changes in environment and feeding practices, etc.). Working for long periods of time on hard surfaces has been named as a cause (road founder); even drinking cold water following work on a hot day has been suggested. Unilateral (one limb) laminitis can occur with prolonged and unequal weight bearing (for example, a horse recovering from a painful fracture on the opposite leg). Pituitary adenomas (benign tumor of the pituitary gland) can affect the normal production of certain hormones. Older horses with this problem have a higher incidence of laminitis. An equally large category of causes is simply unknown. Many horses, to the best of the involved horse owner’s knowledge, are found in this state with no history of illness, change in environmental or nutritional status, etc.
The above is a simplified and brief summary of the damage and causes, but it should be apparent that a multitude of initiating factors exists. It also provides the investigators a very complex disorder that is difficult to study for the following reason: it is obviously a very complex problem; animal welfare issues rightfully exist that prohibit the wholesale creation of the problem to allow studies because of the pain; horse research is very expensive; and lastly and sadly, horse research is not at all well-supported by the horse-owning public or government (horses are not considered to be either food animals or a necessity). This problem does not have an equivalent in other species. All of the above make investigation difficult.
It is necessary to point out several established facts in order to understand why this is such a frustrating disease to treat and manage. By the time the owner or caretaker is aware that a problem exists (pain, reluctance to move or lameness), the problem is very well established. That is, the pain associated with laminitis follows the destructive process. Thus, a developmental phase exists in the absence of any obvious problems. A study performed decades ago indicated a 72-hour delay, on average, from the initiation of the process until the involved horses were noted as having problems. These were even horses who were being very careful and frequently observed. Although that study involved a particular method to create the disease and does not reflect how quickly or slowly this might happen with other causes, it is important to understand that a lag time definitely exists from the beginning until it is recognized.
Recognition is another problem because it is a function of human observation and thus could be months for turned-out horses living on their own. Pain is not always an accurate measure of the degree of destruction either. In other words, a given “victim” could appear to be fairly comfortable and still have significant and permanent damage. Horses can sustain very little lamellar damage and regain soundness because healing, if it does occur, is often incomplete. This means that the tissue arrangement and thus strength of the suspension is often permanently lost. Therefore, the foot remains a mechanical risk and is likely to be a problem in the future. Recurrence and other foot-related conditions (for example, wall separation, foot abscesses and sole bruising) may follow the original episode. Some horses with laminitis may have other problems, which mask the diagnosis such as colic, diarrhea, central nervous system disorders, etc., and thus the diagnosis is not made at the time. There appears to be no age (with the exception of the problem being rare in young horses) or sex predilection, although certain breeds, body types and usage appear to have a higher incidence (ponies, Morgans, heavy show horses, gaited horses with excessively long feet, Standardbred stallions and others). And lastly, it is a fact that no one treatment or combination of treatments for this problem exists that uniformly provides good results.
My observations through the years, which may or may not be correct, indicate the following: a likely candidate for laminitis is the under-worked, overweight individual. Besides being overweight, these horses are basic “apartment-dwellers.” Show horses (and other sports requiring little in the way of fitness), broodmares and stallions (especially Standardbreds) are at risk. Racehorses, endurance horses, three-day event horses and wild horses have, in my experience, a low incidence. Ponies with laminitis are generally easier to manage than horses; Thoroughbreds and Arabians are generally harder to manage, as there is very little foot to work with. Overweight Quarter Horses on the show circuit are, in my opinion, quite susceptible and difficult to manage. Horses with prolonged and serious illnesses (problems like colic, diarrhea, uterine infections and retained membranes following foaling are particularly high on the list) are at a significant risk of developing laminitis.
It is important to state and understand that horses do not read anyone’s notes, books or e-mails, thus the presenting signs I discuss next are generally but not always what is observed. Most affected horses are reluctant to move, especially when turned. The front feet (which are usually the most often involved) may be more difficult to pick up. Generally the discomfort is greatest in both front, although one may be worse than the other. The pulse is usually bounding (stronger pulse pressure than normal) and is best appreciated where the superficial artery passes over the back of the fetlock on both sides. The more painful horse may adopt an abnormal stance (hind and front feet positioned in front of the usual vertical plane). Usually resentment or a painful response to pressure from hoof testers exists just in front of the tip of the frog. Again, it is important to point out that these signs will vary from one horse to the next. A useful cliché exists: horses showing a sudden onset of lameness in either front or all four feet are foundered until proven otherwise. Beware that the signs of laminitis can easily be masked or missed by the situation or disease that created the event (colic, for example).
WHAT SHOULD YOU DO?
The very first thing to do is call your veterinarian. The second thing to do is call your veterinarian! Attempt but do not force the horse into a comfortable environment. What not to do? Do not do anything without instructions. Do not treat the problem yourself with advice from your neighbor, your stacked collection of horse magazines, your Merck Veterinary Manual or advice off of the Internet. Do not pull the shoes unless instructed to do so by a professional. Avoid shipping the horse unless you have no choice. Always keep in the forefront of your mind the fact that something happened to trigger the event, and therefore inexact or inappropriate treatment of the laminitis problem could potentially be harmful to the success of correcting the disease process that helped create the laminitis. This is not a time to “Play Vet!”
WHAT TO EXPECT FROM THE VETERINARIAN
The process will begin with a general physical examination and application of diagnostic techniques to determine the diagnosis or diagnoses. The total picture is important because something happened to create the disorder. This process will involve a discussion of recent history in the horse’s life in an attempt to discover the initiator. In many instances, the cause will elude the owner and examiner. Radiographs (X-rays) of the involved or suspected feet will usually be part of this examination. It is important to point out that an absence of radiographic evidence at this stage of the problem does not mean the horse is not foundered – recall the lag-time aspect of this disease process (that is, significant chemical and molecular damage occurs before structural changes are apparent and thus changes apparent on an X-ray film).
The initial treatment can and should vary with each case, because no two horses or situations are alike. If the originating disease is present, treatment will be designed in an attempt to manage it. Attempts will be started to control pain; the choice of medication will vary. Diet and environmental concerns should be addressed. How the involved feet are handled will depend entirely on the individual case and foot. This could include shortening the toe length; applying Styrofoam, taped-on pads or boots; corrective shoeing or staying with the present shoeing – it always varies. Other treatment considerations may be delayed until the films are interpreted, laboratory results are received and response to day-one treatment is evaluated.
As the case develops, treatment and management evolves and is determined by assessing the degree of damage, pain, farrier expertise, costs, local environment and availability and willingness of labor. Be fully aware that any “battle plan” may have to be altered to suit the changing situation and that the process has a significant head start on treatment.
First of all, very little factual information exists with regard to assessment of the various treatments and management practices that have been utilized. In some cases, the degree and severity of damage exceeds the ability to fix it or comfortably live with it. Regardless of the therapy used or even the success of such therapy at the time, recurring foot problems are very likely. Treatments can be expensive especially over time. Individual cases can be very labor intensive. It is best to think in terms of hoping for a comfortable existence as opposed to a return to normal and athletic function.
The varieties of treatments in the chronic case with structural damage are quite varied. Multiple methods and techniques exist with regard to corrective trimming and shoeing. Hoof wall reconstruction techniques have existed for years, but with wide variation in outcomes (in some cases the situation is made worse). Cutting the deep flexor tendon, in selected cases and sometimes temporarily, can attain mechanical relief. A myriad of chronic-use medications have been used to decrease pain (the most commonly used would be phenylbutazone “bute”) but one should be aware that most any medication used on a long-term basis could potentially create other medical problems. It is also important to note that even within the same foundered horse the selection of treatments and management may vary between the feet. Consideration for the surface (living environment) may be key to successful management. Surfaces may include dry beach sand, peat moss, rubber, gravel-like materials and other reasonably forgiving products. The bottom line is simply that no one system of shoeing and care has successfully surfaced as being best.
LONG-TERM CONSEQUENCES OF LAMINITIS
Toe wall separation (seedy toe) and deformities (usually in the form of parallel rings) are a common sequella. Sinking of the coffin bone within the capsule is a very difficult consequence with regard to treatment and management. In some instances, depending on the degree of rotation or displacement of the coffin bone within the hoof capsule, penetration of the sole by the tip of the coffin bone occurs. This is also a very difficult and life-threatening complication. Such an event invariably leads to bone infection. In some advanced cases, complete loss of the hoof capsule occurs. Deformity of the lower limb (contracture) is not unusual in those horses chronically affected. Perhaps the most common situation is that of recurring pain and lameness – recall that the suspension system may be permanently affected, creating a mechanical problem. Sole-bruising and abscess formation under the hoof wall and/or sole occur with some frequency. In summary, because of the damage to the laminae and the often-experienced incomplete healing, a variety of problems can occur with foundered horses.
Laminitis is a very unique problem. It is one of the most difficult problems facing the horse world. In the event that you as an owner experience this problem with your horse, get veterinary help quickly. Recognize that each case is different and thus these are very difficult problems to manage.
Reprinted with permission from the AAEP, American Association of Equine Practitioners.