Laminitis is a common lameness and health condition impacting a large percentage of horses from many disciplines. It is a condition which most horse owners and veterinarians fear and even despise, mainly due to the ongoing level of care that is required and additionally, the poor prognosis. Laminitis in the horse is a complex condition and considering this, there is no one thing that can be done to remedy the problem. The pain, discomfort, and amount of coffin bone rotation can vary significantly between patients. When you are able to see the whole problem present, then solutions to better manage the condition become more apparent. Then, through this level of understanding, rates of success can improve.
When the word ‘laminitis’ is spoken to a horse owner, almost automatically the emotion of fear begins to take hold. The reason is evident and is mainly due to the poor prognosis that most cases carry. Laminitis is likely close behind colic for reasons of euthanasia in the horse. Fear is one emotion that needs to be eliminated when dealing with a laminitic horse. What is needed is understanding of the process at hand, but despite knowing the process, frustration can quickly set in because of seeking newer solutions.
Laminitis in the horse can be due to many different causes, but for the sake of this discussion it will be classified into 2 main groups; acute and chronic. Acute, by definition, applies to any health or lameness condition that has been present for less than 30 days. Chronic, by definition, applies to any health or lameness condition that is present for 30 days or longer.
Acute laminitis cases in the horse are usually due to a toxic or infectious event or contralateral limb lameness conditions. These cases generally accompany an already sick or compromised patient, and the laminitic events are usually rapid and can be extremely painful. They are the most difficult of all laminitis cases to contend with as a veterinarian, farrier, and horse owner. These equine patients are generally the ones with the highest euthanasia rate due to quickly deteriorating circumstances.
Chronic laminitis cases are more often related to endocrinological conditions, including metabolic syndrome, insulin resistance, and Cushing’s syndrome (PPID). Although these horses may appear normal one day, and lame the next, they are not considered acute in nature. The reason being is that their underlying metabolic related conditions have often been present for many months if not years, and the laminitic events are secondary, not primary.
Laminitis and Rotation of the Coffin Bone in the Horse
Most owners are familiar with the general association of perceived rotation of the coffin bone and laminitis. In the normal horse, when the foot is radiographed, the position of the dorsal aspect of the coffin bone is parallel to the hoof wall.
In the laminitic horse, the two are not parallel but instead, there is now an angle created by the separation of the two. The angle between the two structures is the angle of rotation of the coffin bone.
During the condition of laminitis, by definition, there is inflammation of the laminae, which is the inner tissue of the hoof wall which connects to the tissue overlying the coffin bone. The laminar tissue interdigitates with the bone, essentially holding it in place within the hoof capsule. This is very similar to a zip-lock bag type of attachment.
As laminitis develops with inflammation of the laminar tissue, the connection begins to break down. Over time, the zip-lock bag connection begins to unzip and the connection between the coffin bone and dorsal hoof wall loosens. The deep flexor tendon on the back of the leg in the horse attaches to the bottom of the coffin bone. The normal position of the coffin bone is maintained due to equal connection to the dorsal hoof wall and the backward pull of the deep flexor tendon. When the dorsal hoof wall attachment begins to fail, there is very little to counteract the deep flexor tendon pull, and over time, the coffin bone begins to rotate or shift downward. This is in conjunction with laminar or wall separation often not just in the toe but extending into the quarters, especially in the chronic cases.
Clinical Signs of Laminitis in the Horse
Typical clinical signs of laminitis in the horse are directly reflective of the laminar inflammation, loss of laminar connection (tearing), and malpositioning of the coffin bone (rotation). Given the nature of the events, this leads to increased pain in the toe region of the hoof and in most cases involves the front feet. The reasoning for this is that laminar inflammation likely occurs in all four feet, but due to the horse bearing 2/3 of their body weight in the front, it increases the load on those limbs and increases the damage.
Due to the pain in the toe region, the affected horse often stands rigid with their feet placed more out in front of them, rather than directly under. This stance helps to alleviate stress upon the toe while shifting weight more to the heel. Many of these horses are viewed as having a ‘saw-horse’ type of stance. Dependent on the level of discomfort, there is variable foot placement forward. Some horses are very rigid and reluctant to even take a step forward, while some others are mild, being less rigid and more willing to walk forward.
Upon examination of the laminitic patient, when evaluating the feet specifically, it is very common to have increased digital pulses to the foot and increased pain in the toe, when applying hoof testers. In addition to the foot examination, in most cases the horse is obviously stressed and uncomfortable with an elevated heart rate, respiratory rate, and in some there is evident sweating and distress. Dependent on the origin of the laminitic event, there may also be an elevation in body temperature due to infectious causes. Blood work is often performed which is often normal, but in some patients, there is evident problems including dehydration, alterations of the white blood cell counts, and abnormalities in organ function.
Causes of Laminitis in the Horse
Laminitis is a systemic health condition in the horse and is not just isolated to the feet. Laminitis indicates that there is inflammation of the laminar tissue, but this inflammatory response is often triggered at a remote distance in the body, but clinically obvious in the feet at that point in time.
Most cases of laminitis can be attributed to one of three mechanisms:
- endocrine/metabolic origin
- infectious or toxic event
- supporting limb lameness
Dependent on the origin of the laminitis, or cause, the severity and rate of progression in the patient can vary significantly. All conditions or causes result in an inflammatory response within the patient, but the magnitude of the inflammatory response will dictate the severity.
Supporting limb lameness induced cases of laminitis can be very slow in onset. These types of cases are compounded by two ongoing factors; pre-existing high levels of inflammation and increased weight distribution to a specific limb. A perfect example of this form of laminitis was demonstrated in the case of the famous race horse, Barbaro. Due to the fracture of the hind limb and inability to apply full weight to that limb over a long period of time, increased weight was redistributed to the fore limbs to compensate. The ongoing inflammatory response associated with the bone fracture and likely other health ailments, including gastrointestinal dysfunction, predisposed this horse to circulatory and tissue changes in the entire body and to the feet. Then, more problems are created as increased weight is applied to the forelimbs, further stressing an already fragile situation. These cases are common with bone fractures but can also develop secondary to ongoing foot problems on various levels or even soft tissue injuries or joint conditions. If ongoing weight redistribution is occurring, then those limbs taking on the additional weight are at risk of developing laminitis. This type of laminitis can be ongoing with variable levels of pain and discomfort for the horse. They are often a real challenge to manage, mainly because the primary injury causing the weight distribution needs to be addressed equally.
Infectious and toxic type of events creating laminitis in the horse can be extremely challenging and serious, resulting often in euthanasia for the patient. The exact causes or origins of the infection or toxin can be numerous but include grain overload, uterine infections in mares, septicemia due to various internal infections, colitis and colic events, toxin exposure, and exposure to xenobiotics which includes certain medications such as antibiotics and corticosteroids. The exact mechanism of action can vary whether if it is an endotoxic/septicemic type of event, influence of corticosteroids, direct toxemia and damage to organ function, or shift of the gastrointestinal microbiome as seen with some antibiotics. In many of these cases, endotoxemia is a direct result, which is due to a microbiome shift within the digestive tract, creating increased permeability (leaky gut), and release of endotoxin into the general circulation. This endotoxin then elicits a tremendous inflammatory response in the patient, which can impact every aspect of health, including the health and circulation to the hoof laminar tissue. Many of these cases are amendable and responsive to therapy, but many due to the level of the inflammation response, progress very rapidly and necessitate euthanasia. The act of euthanasia is warranted due to intractable pain, and often penetration of the coffin bone through the sole due to rapid rotation.
Endocrinological or metabolic related causes of laminitis are the most common, creating a high majority of chronic laminitis cases, more than acute. In most of these cases, the horses are overweight, and have been overweight and out of normal body condition for quite some time. In all cases of laminitis, there is an inflammatory response which is triggering various cellular events in the body. The difference in the rate of progression of each type of laminitis is dependent on the severity of that inflammatory response. In the endocrine or metabolic type of patient, the inflammatory response is present and above a normal level, but it is like a smoldering fire rather than a blazing one. The inflammatory process begins as the weight increases in the patient, mainly since increased fat deposits secrete their own inflammatory proteins, termed adipokines. As this inflammation progresses, there are often also underlying digestive concerns creating more inflammation and contributing to the problem, which include leaky gut syndrome and microbiome imbalance. This level of inflammation continues to build over time, and soon, cellular events and function are altered. This may be evident as an altered insulin response, leptin response, adrenal and pituitary function, which are all commonly diagnosed. As these cellular functions are impaired, then tissue health becomes compromised as does circulation. The hoof health is not ideal, growth is impeded, circulatory changes to the feet are compromised, and soon, coffin bone rotation is evident along with laminar separation.
These cases often go on for years, having good months or seasons, and others not so good. These horses tend to be more sensitive to the carbohydrates present in various food sources, mainly due to the fact of the influence of inflammation on those cell functions and the changes in the gut microbiome. The rate of coffin bone rotation or laminar separation is often very steady, changing slightly one way or the other with each year. They can be a challenge to manage, but out of the three classifications, these are usually the most responsive with the right approach.
Inflammation; The bottom Line Connector in Equine Laminitis
Laminitis in the horse is an ongoing challenge for horse owners, veterinarians, and researchers. Despite the vast amount of research given to laminitis, we have learned a lot regarding cellular pathways involved, but little regarding pharmaceutical therapy options. This will likely continue for many decades, until we step back and look at the bigger picture. Instead of isolating the problem just to the feet, we need to look at the whole horse, realizing that there is more to the story and likely the events in each patient may be due to different causes or origins.
Inflammation is the bottom line connector and research strongly points us in this direction. There may be many cellular pathways or inflammatory proteins mentioned, each creating their own negative effect on health or circulation, but the bottom line is that they are all related to the inflammatory cascade. The process is present in each case, no matter if it is a supporting limb condition, infectious or toxic event, or endocrine in origin. Inflammation is there, but on different levels. The higher the inflammatory response, the more acute the condition, and the more rapid the events unfold. This is the difference between a septic colic case with laminitis and a metabolic syndrome patient. One unfolds in a matter of days, while the other smolders over a period of years.
In almost all cases of inflammation, there is a direct link to the digestive tract on some level, whether if that is primary or secondary. The digestive tract, when out of balance, results in a dysbiosis or shift in normal bacterial populations. In many cases, there are overgrowths of potentially harmful bacteria that are normally present in smaller numbers, which makes the overall population of bacteria less diverse. One type is gram negative bacteria, including E. coli and Salmonella species. As these bacteria increase in number, they gain access to the general blood circulation due to impaired gut permeability. The bacteria release LPS, or endotoxin, which then often instigates the inflammatory response in the patient. This is termed endotoxemia and the level can vary from one patient to another. A horse with Salmonella associated colitis often has a very high level with acute symptoms, while a horse with metabolic syndrome has lower levels and more chronic symptoms. In other studies and research, the dysbiosis is often related to overgrowths of Lactobacillus and Group D Streptococcus bacteria. This again leads to a less diverse bacterial population within the digestive tract. This phenomenon isn’t just present in a few cases of laminitis, but likely is present in all cases on some level, which indicates gut problems. Again, this can be primary or secondary.
The ultimate challenge comes in managing that inflammatory response, which can differ from one patient to another. Current pharmaceutical therapeutics only target specific pathways of inflammation, only going after the effects, rather than the cause. If we step back in each case and find the cause of that inflammation, our outcomes may be more optimal. This is not easy in the case of colitis or ingestion of a toxic substance, but if we apply a different mindset, the outcomes could possibly improve even in those acute cases.
We will discuss therapy options in another article.
Author: Tom Schell, D.V.M., CVCH, CHN