What is laminitis?
Laminitis is a crippling and painful condition of the horse's foot. Affected horses are recognized based on lameness, stiffness, reluctance to move and prolonged recumbency. It usually affects more than one foot at a time. The laminitis disease process affects the connective tissues ("lamellae"), which attach and connect the inner lining of the hoof capsule to the coffin bone (the bone at the bottom of the horse's leg). Disease of this connective tissue is very painful and, in severe cases, may lead to disattachment and structural compromise.
What is "founder"?
The term "founder" is commonly used synonymously with laminitis. However, in the opinion of some veterinarians, the term "founder" should be reserved for those horses in which the attachment of the inner lining of the hoof capsule to the coffin bone, has actually broken down and caused the coffin bone to change its position within the hoof. The weight of the horse is important in this respect, as it contributes to the distraction process through the deep digital flexor tendon.
Predisposing Factors
Obesity. Heavier horses are at increased risk for severe laminitis because more stress is put on the lameinae
Certain plants. Ingestion of endophyte-infected Tall Fescue has been proposed to increase the risk for laminitis.
Hypothyroidism. Numerous hormonal imbalances have been proposed to increase the risk for laminitis. Other than elevated cortisol levels, no other hormone in excess or deficiency has been shown to cause laminitis. There is no evidence that hypothyroidism causes laminitis, but some obese horses have low levels of thyroxine. The reason is unknown.
Whole body potassium deficiency. Some diets may not provide sufficient potassium and might increase the risk for laminitis.
Stress. Stressful events lead to enhanced endogenous cortisol production that appears to lead to laminitis.
Hoof conformation/farriery. Small feet in relation to the size of the body and other poorly characterized hoof conformational changes may affect the likelihood of laminitis. Excessive farriery, especially coupled with hard work on hard ground, represents a big risk for laminitis.
Age. Laminitis probably never occurs in horses less than 10 months of age.
Breed/genetics. Miniature breeds do not appear to be at risk for laminitis.
Concrete and paved surfaces. Horses that spend substantial periods of time on very hard surfaces appear to be at risk for laminitis.
Previous lamellar disease. Any horse is at increased risk for further bouts of laminitis after developing the disease in the first place. This is especially true of earlier bouts of laminitis.
Use of certain drugs. Glucocorticoid steroids such as dexamethasone and triamcinalone appears to lead to laminitis.
It is likely that laminitis may arise as a consequence of numerous different causative factors. Most current information pertaining to the cause of laminitis is based on the laminitis seen in conjunction with intestinal disorders. However, it should be noted that laminitis sometimes occurs in the absence of any intestinal problem and may, in those cases, have an entirely different mechanism.
Some of the well-recognized causes for laminitis are:
Intestinal. Associated laminitis is an intestinal problem that leads to the absorption of specific toxic substances into the bloodstream that cause laminitis. Numerous intestinal problems may cause laminitis and include diarrhea (colitis), colic, ingestion of lush grass, and the consumption of excessive quantities of grain.
Plant Toxins. Several plant species may cause laminitis. Well known examples include Black Walnut and Hoary Alyssum. Horses that are allowed to graze endophyte-infected Tall Fescue are believed to be at increased risk for laminitis. Other unrecognized plant species might also cause or increase the risk for laminitis.
Trauma. Whenever a hoof has been severely traumatized, the resulting inflammation may lead to laminitis. Examples include "road founder," the development of laminitis following hard work on hard ground. (Road founder is important in horses with recently trimmed soft feet that have not been shod). Laminitis occurs in some horses following aggressive trimming, even in the absence of any substantial work.
Bearing Excessive Weight. Whenever a horse must bear all (or most of) the weight of one side of the body on one foot, that foot is at great risk for laminitis. An example of this type of laminitis is the situation that exists when a horse is lame in one limb to the degree that the weight is predominantly borne by the opposite limb. Oftentimes, before the source of pain in the original limb has healed, lameness is evident in the weight-bearing limb because laminitis has occurred as a result of the extra loading.
Inflammation. Another cause is the extension of the inflammatory process during the development of a sole abscess.
Vasculitis. Laminitis may occur during or following recovery from a respiratory infection. Although it is uncommon, some of the infectious agents involved in equine respiratory disease will attack the blood vessels (vasculitis) and, in so doing, interfere with blood flow through the hoof, leading to laminitis.
Glucocorticoid Steroids. For inexplicable reasons, glucocorticoid steroids appear to cause or increase the risk for laminitis in horses. For this reason, this category of drugs is used cautiously in horses. The body's production of its own natural glucocorticoids (cortisol) is sometimes increased (during stress) and this increase in endogenous cortisol appears to lead to laminitis. The syndrome of excessive glucocorticoid effect in the body is known as Cushing's syndrome; laminitis is one of the important clinical manifestations of equine Cushing's syndrome.
Idiopathic. In many instances, a specific reason for the development of laminitis cannot be clearly identified. It is likely that an unseen/unrecognized, mild intestinal disturbance or dietary indiscretion may be the cause.
What to Watch For
The fore feet are much more commonly affected that the hind feet, and the most common clinical presentation includes signs of lameness and stiffness. You may notice the following:
Severely affected horses exhibit reluctance or refusal to move when prompted. The pain of laminitis is sufficiently severe as to cause affected horses to prefer to lie down for protracted periods of time.
There is a characteristic stance and gait – affected horses tend to attempt to bear more weight on their hind feet to protect the fore feet and, in so doing, tend to draw their center of gravity back over the hind feet. The hind feet occupy an unusually forward position under the body (when standing and when moving). The fore feet tend to be pushed forwards in front of the body such that weight bearing is shifted into the heel area of the affected feet.
There is marked reluctance to permit feet to be picked up because the opposite hoof is so painful when bearing weight.
There may be soft tissue swelling under the skin of the lower limbs and an apprehensive facial expression (pain).
There may be inappetance, colic, and weight loss.
In time, the presence of laminitis leads to abnormal growth of the hoof wall. Disturbances in the growth of hoof wall can be appreciated on inspection of the growth rings that run around the hoof wall. In addition to the growth rings, the sole of affected feet tends to be "dropped" (convex) and the laminitic process has widened the white line zone (at the sole). With substantial weight loss, pain, and protracted recumbency, many decubital ulcers (skin erosions) typically develop at the points of bony prominences.
It should be noted that severely laminitic horses often appear to be exhibiting neurological signs or signs of abdominal pain (colic). In actual fact, they are in so much pain as a result of inflammation in their feet. Some laminitic horses tend to shake their painful feet – especially those affected in the hind feet.
Laminitis is usually diagnosed based on the symptoms. The physical examination may show marked prominence of the digital arterial pulses and further evidence of pain, such as elevated heart rate and elevated respiratory rate. If the disease has been present for a considerable period of time, your veterinarian may notice abnormal growth of the hoof capsule, dropped sole, and a widened white line zone.
The diagnosis of laminitis is usually established by the following criteria:
Typical clinical signs (symptoms)
Appropriate clinical setting (one might expect laminitis to arise during treatment of some diseases – such as diarrhea)
Painful reaction to hoof testers at toe. Application of pressure using "hoof testers" at the toe of the laminitic hoof will often (but not always) elicit a painful reaction. In some cases, an abscess develops in the affected lamellae and might drain out through the sole or drain through the coronary band.
Increased prominence of digital arterial pulses
Radiography, although laminitis may be present without ANY radiographic abnormalities. It is strongly recommended that a radiographic examination of the affected feet should be undertaken as soon as possible when laminitis is suspected. In some cases during the early stages of laminitis, there are no abnormalities evident on radiography.
However, radiography is advocated because it is typically important to:
Determine whether this new pain represents a new event or reactivation of a preceding laminitic attack (chronic laminitis)
Establish a baseline upon which the effects of treatment can be judged (is it getting better or worse or staying the same)
Help assess the prognosis – the more severe changes (based on radiography) tend to be associated with a poorer prognosis.
Assist in the direction of treatment strategies that include special trimming, farriery, and removal of the hoof wall at specific locations
It is not usually necessary to anesthetize the affected hoof in order to make the diagnosis. Obviation of pain may result in severe damage (new or further separation of the coffin bone from the lining of the hoof wall) and exacerbation of lameness if the horse is exercised excessively. Although it is severe, the pain actually "helps" to prevent the affected horse from causing further damage to compromised lamellae.
The most common reason that laminitic horses fail to make a good recovery is because the horse is allowed to self-exercise too soon; it is common for affected horses to be "turned out" sooner than 6-8 weeks following initiation of treatment. These horses have often been stall-confined for several weeks (during treatment). Much too soon, they are turned out and (in light of their recent confinement) allowed to run around. Neither the owner nor the horse has any appreciation for the fact that the lamellar attachments have not completely healed. Although the horse perceives that his feet are okay, the weakened attachments can all too easily be re-damaged – leading to a major "flare-up" and worsening of the underlying disease process.
The specific treatment should be determined by the veterinarian who has examined the horse based on his findings and results of radiography of the affected feet.
Treatment
Treat the primary problem if it can be identified
Rest
Application of hot or cold (depends on stage)
Appropriate pain relief
Thickly bedded stall
Drugs aimed at improving the blood flow to the feet (such as nitric oxide donors, acepromazine, pentoxifylline)
Drugs used to reduce inflammation which can develop when blood supply is poor (DMSO)
Frog support
Heparin therapy
Aspirin
Change the angle of the painful hoof
Use of frog support
Special trimming and farriery – chronic cases
Surgery (transect the DDF tendon)
Other than the pain relief and the antiinflammatory properties of non-steroidal anti-inflammatories, (bute, banamine, ketofen), no drug has been shown to affect the course of laminitis. Despite years of research, this disease continues to defy solutions, and that is likely due to the fact that it can either be too late by the time symptoms are present, or the underlying problem has not been fixed.
Special Points
Most affected horses are prone to further bouts of laminitis.
Most affected horses do not re-achieve the same level of performance that they had prior to developing laminitis.
Horse owners often undertake treatment without fully appreciating the potential cost (based on length of time and cost of drugs) and labor needed to care for affected horses. Many of those horses show episodic improvement during treatment, but overall continue to deteriorate.
Most veterinarians would agree, that laminitis is one major cause of suffering in horses, and it is difficult to know when to give up. Certainly, if the horse does not respond to pain medication, is relatively immobile, doesn't eat, has side effects of pain medication, if there is serious rotation of the coffin bone, hoof wall destruction, or infection, euthanasia should be considered.
These horses are suffering with little hope of relief. Eventually they will go down, and not get up. Although euthanasia is an extremely difficult decision, the picture is perhaps clearer with laminitis that with other diseases. You might want to set-up criteria for "suffering" and "indications for euthanasia," which may sound a little morbid, but if you put it on paper, that means you've thought about it. Talk it over with your veterinarian. They will be impressed and glad to help you further.
Prognosis
The prognosis is unpredictable, and it may be (and should be recognized as such) grave in some severe cases. Few "recovered" (remissive) horses will be able to work at a high level of performance.
