The Fight to Conquer Equine Laminitis
- Jan 1, 2011
Teams of veterinarians and farriers from around the country gathered at the fifth International Conference on Laminitis and Diseases of the Foot in Monterey, Calif., Sept. 17-18, 2010, to discuss the most cutting-edge information available for the fight to conquer laminitis. This devastating hoof disease is caused by an inflammation of the horse's laminae--interlocking leaflike tissues attaching the hoof to the coffin bone. The exact causes, treatment, and prevention methods are varied and often elusive, but the presenters featured at the conference provided more insight on topics such as diagnostic testing, management strategies, and the importance of nutrition, exercise, and hoof care for the laminitic horse.
Following are synopses of some of the conference presentations. Longer versions of these articles can be found on TheHorse.com.
Preventing Laminitis in At-Risk Horses
Even though veterinarians and farriers are making progress in developing laminitis treatment techniques and researching the causes of laminitis, prevention is still the No. 1 defense. Bob Agne, DVM, an equine podiatrist at Rood & Riddle Equine Hospital, in Lexington, Ky., discussed how to recognize individuals that are at risk for laminitis and how to manage them to reduce the risk of the disease.
Several pre-existing conditions can put a horse at risk for laminitis, Agne reported. He noted risk factors and preventive treatments for each, but he cautioned that every case is different.
Equine Metabolic Syndrome (EMS)
- Typical clinical signs: Easy keepers; overweight horses with cresty necks and discreet subcutaneous fat deposits; and high insulin and glucose levels.
- Possible laminitis prevention protocols: Restricted carbohydrate intake, controlled exercise, limited grazing during long hours of sunshine and cool temperatures, levothyroxine supplementation (for weight loss), glucose and insulin testing in spring and fall to check the blood for a hyperinsulinemic state (high levels of the hormone insulin that predispose horses to laminitis), and metformin (an anti-diabetic drug) administration if insulin levels rise above 100 uU/mL.
- Typical clinical signs: Cushing's disease is caused by a slow-growing, noninvasive tumor in the pituitary gland and typically only occurs in horses over 13 years of age. Unfortunately, laminitis is often the first clinical sign, which makes prevention challenging. These horses also exhibit rough, excessively long hair coats and can have high circulating levels of adrenocorticotropic hormone (ACTH). Affected horses can also have high levels of blood insulin and glucose.
- Possible laminitis prevention protocols: Annual ACTH, insulin, and glucose tests for horses over 13; pergolide medication for horses with high ACTH and hyperinsulemia/hyperglycemia or for horses showing excess body hair and laminitis; diet, exercise, and grazing protocols as per EMS; and metformin in some cases.
Prior Bouts of Laminitis
- Typical clinical signs: a distorted hoof capsule, stretched white line, and abnormal foot radiographs showing coffin bone rotation.
- Possible laminitis prevention protocols: Identify and address cause of previous bout, shoe and trim to encourage growth of the sole, and remain vigilant for the earliest signs of recurring laminitis. Additionally, yearly foot radiographs can help identify any changes in the hoof.
Foot Infection and/or Inflammation
- Typical clinical signs: Lameness, swelling, draining tracts, heat, and increased digital pulse are evidence of inflammation that can compromise lamellar tissue.
- Possible laminitis prevention protocols: Radiograph feet with chronic draining abscesses or horses whose comfort level doesn't improve in a few days after abscess drainage. A contrast study of the area of infection called a fistulogram can be used to determine the extent of the damage. Addressing abscesses promptly and treating severe ones aggressively are important for preventing lamellar failure. Finally, protecting the wound to avoid reinfection and using a wedge heel and rocker-toe shoeing will help to reduce stress on dorsal laminae.
Contralateral Limb Laminitis
- Cause: A non-weight-bearing lameness results in an increased risk of laminitis in the opposite foot. This is caused by reduced blood flow within the foot that is forced to bear all of the weight.
- Possible laminitis prevention protocols: Treat the underlying cause of the initial lameness as quickly as possible; use material to help support the contralateral foot, especially the frog and sole region; remove the shoe if the foot is long, the shoe is inappropriate, and/or lameness is unlikely to improve quickly; and elevate the heel. Finally, monitoring the foot frequently by assessing digital pulses, coronary band health, and venograms are all important for preventing and detecting contralateral limb laminitis.
If laminitis does occur, early intervention can help you minimize the disease's effects. The more owners learn to recognize the warning signs of laminitis, the more quickly the disease can be treated and damage to the laminae can be minimized.
Understanding Nutritional Risks in Laminitic Horses
We might be feeding our horses too well, at least as far as predisposing them to laminitis. Ray J. Geor, BVSc, PhD, Dipl. ACVIM, professor and chair of the Department of Large Animal Clinical Sciences at Michigan State University, spoke about controlling nutritional risks in pre- and post-laminitic horses.
"All of us recognize that horses evolved to consume roughage," said Geor. "Despite the fact that we're all well aware of that, we tend to feed horses somewhat differently. We often feed them starch-based meals (cereal grains and sweet feeds, for example) or allow them to graze 'improved pastures' that are rich in sugars."
Overconsumption of these types of feeds can lead to laminitis, especially in horses and ponies with equine metabolic syndrome. Changes in pasture, like those that occur in spring and fall when the water-soluble carbohydrate (WSC) and starch contents rise, pose the greatest risk for an episode of laminitis.
Geor listed three key concepts related to risk of nutrition-related laminitis:
1. Substantial flow of rapidly fermentable carbohydrates (i.e., starch and WSC) to the hindgut can occur with grain feeding and pasture grazing under certain conditions, leading to changes to and instability of the microbial community living in the hindgut. Reduction in the size of grain and grain-based meals and restricted pasture access at certain times of the year can help reduce diet-associated disturbances in hindgut function.
2. Dietary starches and WSC markedly affect blood-insulin responses, and equids with EMS tend to have exaggerated responses. Very high blood insulin is one factor that contributes to development of laminitis in EMS animals.
3. Seasonal factors can modify the risk for nutritionally associated laminitis through effects on appetite, adipose (fat tissue) mass, insulin sensitivity, and the dynamics of blood insulin.
Geor added that carbohydrate nutrition is strongly linked to laminitis risk, and that strict management of carbohydrate nutrition is indicated for equids with an insulin-resistant phenotype (i.e., EMS).
Platelets Might Play Early Role in Laminitis
Laminitis begins well before clinical signs occur, at the cellular or even the molecular level, and addressing platelets might be a key to prevention or early treatment. Inflammation is central to most cases of laminitis, and Jamie Textor, DVM, Dipl. ACVS, an equine surgeon and PhD candidate at the University of California, Davis, discussed cellular events that happen before that inflammation manifests itself in clinical signs.
The components of laminitic inflammation at the cellular level are neutrophils, platelets, and monocytes. Textor focused on platelets because research indicates that they are inflammatory cells, are very sensitive to endotoxins, and might be the first responders in laminitis.
When platelets activate, they aggregate or clot and then change shape radically. They also contain and release vaso-constrictors, and that restriction of blood flow in the foot could lead to laminitis.
"We've got a triple threat here," said Textor. "We've got our platelets activating early, probably the very first response. We've got the neutrophils (a type of white blood cell) getting activated. They start interacting with the endothelium (lining of blood vessels) and start to go across it (into the laminae). After that time, laminar breakdown begins."
Knowing this sequence of events might allow veterinarians to develop therapeutic strategies. "We could prevent these cells from ever getting (to the laminae) or ever being activated," said Textor. "We could block the things that they deliver--we could prevent the vasoconstrictors from doing their thing. Lastly, maybe we could enhance the protective mechanisms that tissue might already have in place."
Equine Metabolic Syndrome and Laminitis
As noted in an earlier presentation, horses with EMS are at a higher risk for laminitis than the average horse. Thomas J. Divers, DVM, Dipl. ACVIM, ACVECC, professor and chief of Large Animal Medicine at Cornell University, spoke about the correlation between EMS and laminitis and discussed the management of these cases.
Genetics, diet, and exercise are the three factors that can best determine a horse's risk for EMS. Those that develop EMS are usually five to 15 years old, obese, and easy keepers (horses and ponies that maintain or gain weight on a minimum amount of food), often with a cresty neck. Divers said that the fat in the middle of the neck might contain inflammatory mediators, which could lead to insulin resistance (a feature of EMS where the body doesn't respond properly to insulin, which is responsible for controlling glucose levels, which provide energy to cells).
While researchers don't yet know why EMS horses develop laminitis, they have several theories.
"One of those is systemic inflammation triggered by episodes of carbohydrate overload in the lower GI tract," said Divers. "Another possibility is insulin toxicity. It's possible that insulin affects the normal mitosis (cell division) of the laminae during hoof growth or has a detrimental effect on blood flow to the laminae.
"It's also possible that increased insulin has an adverse effect on glucose regulation within the cells."
Divers said that many early changes in the laminae in EMS horses might go undetected clinically. However, endocrine testing of at-risk individuals can allow veterinarians to catch many cases before structural damage to the laminae occurs, get a better prognosis by identifying/¬treating cases earlier, and monitor responses to treatment.
A recent study on the prognoses of horses and ponies with EMS and laminitis showed that an animal with previous laminitis episodes might not develop as severe clinical signs in a subsequent episode. Divers noted, however, that their long-term prognoses after repeated bouts of laminitis was worse than that those with only a single episode, confirming the importance of early detection and treatment of EMS and associated laminitis.
Understanding Cushing's Can Help Treat Cushing's-Related Laminitis
Because horses afflicted with equine Cushing's disease often develop laminitis, advances in diagnosis and treatment of Cushing's can help veterinarians better prevent and/or treat the laminitis that stems from it, explained Nora Grenager, VMD, Dipl. ACVIM, of the Steinbeck Country Equine Clinic, in Salinas, Calif.
Horses with Cushing's (pituitary pars intermedia dysfunction or PPID) have an eightfold decrease in levels of dopamine (a hormone and neurotransmitter) and its metabolites (breakdown products) compared with nonafflicted horses of the same age. Grenager reported that this is most likely due to localized oxidative stress and noted that evidence is lacking that this decrease is caused by systemic inflammation or systemic oxidative stress. Other, less likely factors that have not yet been well-evaluated could include toxins or pesticides, genetic predisposition, chronic inflammation or abnormal systemic metabolism, and a diet lacking enough selenium or protein. Part of the problem with Cushing's is that it can be difficult to diagnose early because horses can present widely divergent clinical signs.
Grenager discussed common Cushing's tests, particularly the dexamethasone suppression test (DST) and the resting endogenous ACTH test. Veterinarians usually employ these tests in an attempt to diagnose horses that don't show dramatic clinical Cushing's signs.
While the DST can be effective, it requires two veterinary visits and administration of steroids (which can on occasion trigger laminitis in susceptible horses). It can also give early false negatives and show seasonal variations (meaning the horse's response to the test will vary with season; false positives are more likely to occur when testing in late summer and fall). A combined DST/thyrotropin-releasing stimulation test might show fewer false positives, but it is a 24-hour test that requires four blood samples. The ACTH test requires only one vet visit and no steroids.
Grenager likes the newer domperidone stimulation test because it is a safe test that doesn't take long and has been shown to be more effective year-round, avoiding the seasonal variations in test results. It is more expensive, however, and its reliability is not yet well-documented.
Regarding Cushing's treatments, Grenager noted that pergolide is the most effective treatment, but it can be expensive; cyproheptadine is less expensive yet not as effective.
Veterinarians usually prescribe specific diet and exercise regimens for Cushing's horses, which can help minimize the risk of laminitis. Grenager also recommended good hoof and dental care, routine fecal egg count testing (to monitor for parasites), and body clipping if medication is not controlling the long hair coat. She advised watching for clinical signs and diagnosing and treating affected horses as soon as possible to avoid Cushing's-associated laminitis.
Chronic Laminitis Can Increase the Risk of Foot Infection
Because laminitis compromises the equine foot so drastically, horses with the disease are more prone to foot infections and abscesses. Agne discussed how to diagnose and treat such infections.
The structural damage that results from laminitis restricts blood flow to the foot, which makes infection more difficult to fight. Agne said the stretched and scarred white line in laminitic horses is particularly susceptible to infection.
"The scar tissue is moist and lacks normal blood flow and, consequently, is a prime medium for bacterial growth and infection," Agne said.
Hoof infections threaten normal horses as well and usually present with the typical signs of inflammation, Agne said, which include lameness, swelling, heat, draining tracts, increased digital pulse, and/or possible evidence of hoof injuries.
When diagnosing foot infections, said Agne, determine whether they are superficial or also involve deeper structures. That allows a veterinarian to prescribe the best treatment plan and give an accurate prognosis. If the infection involves the coffin and/or navicular bone, coffin joint, tendon sheath, collateral cartilages, and/or navicular bursa, the prognosis will be more guarded. Penetrating wounds (such as nail punctures) are particularly dangerous.
"Evidence of a penetrating wound always carries the possibility of deep infection," said Agne. "Penetrating wounds, especially in the caudal (rear) portion of the foot, are medical emergencies. If they are left untreated for over 12 hours, the prognosis for a return to soundness decreases significantly."
The goals for treating foot infections, Agne said, should be to debride any dead tissue, maintain drainage, apply antibiotic therapy, provide protection, support the surrounding healthy tissue, and protect the contralateral (opposite left/right) foot from laminitis.
Of course, as with all equine health concerns, prevention is the best option. To reduce the chances of a horse getting a hoof infection, an owner should keep the horse on a regular trimming and shoeing schedule, pay close attention to hoof health, and maintain a safe and healthy environment.
Managing Insulin Resistance Through Diet and Exercise
Insulin-resistant horses are prone to laminitis, but owners and veterinarians can often successfully manage them through strict diet and exercise regimens. Geor outlined some of those ¬regimens.
In designing a diet and exercise program, Geor first stressed the importance of a thorough baseline clinical assessment. That includes not only checking body weight and body condition score and blood-insulin levels, but also evaluating the horse's current feeding program, level of physical activity, and soundness.
Set realistic goals for weight loss and develop a monitoring plan. Geor indicated that weight loss of 0.7-0.8% of initial body weight per week over a three- to four-month period is a realistic target.
For weight loss, Geor recommended that the horse have no access to grain, treats, or uncontrolled pasture grazing. Hay or the equivalent is the diet cornerstone, initially fed at about 1.2% of body weight a day. Decrease the caloric content by feeding hay that was harvested at late maturity. Hay can also be soaked to reduce its sugar content. A ration balancer that provides essential vitamins and minerals can be fed along with the hay, typically no more than 1-1.5 pounds a day.
Although there isn't much data available yet from studies evaluating the effects of exercise in obese, insulin-resistant horses, Geor said that exercise most likely helps these animals. He emphasized that an exercise program must be combined with dietary restriction. However, "starting an exercise program in a horse or pony that has had a recent episode of laminitis is tricky because there is a risk of causing more damage to the feet," he noted. Your veterinarian needs to give the all-clear, and the horse must be monitored closely.
Lastly, Geor recommended increased turnout for confined horses in a large dry lot along with structured exercise. Begin with light exercise, perhaps 10-15 minutes a day, three to four days a week. Be sure the horse works on a good (forgiving) surface, and monitor his feet carefully. Then gradually increase the frequency and duration if he is comfortable.
Using Force Measurements to Help Shoe Laminitic Horses
Corrective shoeing for laminitis doesn't always work, despite veterinarians' and farriers' best efforts, and it's not always clear why a particular shoeing job isn't successful. In-shoe force measurements, however, can show the effects of shoeing on the foot, allowing for timely adjustments and improved treatments. Patrick T. Reilly, chief of farrier services at the University of Pennsylvania's New Bolton Center, explained the advantages of taking these measurements in laminitic horses.
There are a variety of opinions on how best to treat each individual laminitic horse, but, Reilly said, "There are two things that we seem to agree on universally in our mechanical goals (for laminitis). One goal is that we want to take some strain off of that lamellar interface ... Secondly, we want to protect the dorsal sole on the surface of the foot (the sole nearest the toe area, which is an area frequently traumatized as a result of laminitis)."
At New Bolton, Reilly and his colleagues have treated many horses at risk for laminitis with convex (arched) solar support. The idea is that putty on the bottom of the foot can help reduce weight bearing by the hoof wall, potentially relieving strain on the compromised lamellar interface. Subsequent force measurements showed that such treatment achieved this goal.
When one of New Bolton's research horses developed laminitis, Reilly used force measurements to investigate three ways to manage the dorsal hoof wall: Leaving the distorted wall extending over the front of the shoe, squaring off the dorsal hoof that extended over the shoe at a 45-degree angle, and blending the hoof wall from the shoe up to the coronary band. Reilly explained that removing this wall seems to affect the structural integrity of the hoof capsule.
First Reilly measured the force on the dorsal solar surface when leaving the wall in place. After he squared off the toe, the force on the dorsal solar surface rose, and it rose again after Reilly removed most of the distorted hoof wall. This suggests there is a possible benefit to leaving this wall to keep the hoof capsule strong and able to withstand the weight bearing and mechanical forces associated with even limited movement.
Reilly noted that another hot topic in shoeing laminitic horses is where to place breakover (the forwardmost point of ground contact when the hoof is on the ground). Reilly conducted a study on six sound horses to see the effect of changing breakover location on dorsal solar forces at the walk and trot. Although the statistical analysis is incomplete, he found that while there might be beneficial aspects to moving the breakover point back, there can also be consequences.
Reilly gave conference attendees two take-home messages: Keep the weight off the dorsal sole as much as possible; and externally reinforcing the hoof wall can often help achieve this goal.
How Hoof-Wall Resections Can Help Laminitis Cases
When laminitis develops to the point that the hoof wall restricts blood supply to the laminae, causing further inflammation, a hoof-wall resection might be needed. Amy Rucker, DVM, of Midwest Equine in Columbia, Mo., spoke about when to perform resections and methods that give veterinarians the best chance for success.
In some laminitis cases the distal (lower) rim of the coffin bone becomes septic (infected) due to compromised blood flow and dying tissues. Rucker explained that fluid resulting from this can travel up the lamellar interface, breaking out at the coronary band. If initial treatment, usually a poultice, doesn't stop the process, the coronary band will swell and prolapse over the hoof wall. The wall then cuts into the swollen tissue, causing further inflammation and restricting blood supply to that tissue.
Performing a resection--literally taking off part or all of the hoof wall--just below the coronet can relieve the pressure on the laminae and thereby allow the critical blood circulation to be restored. With meticulous aftercare, the foot's underlying tissues can then repair.
Rucker noted the following aspects of her hoof wall resection technique:
- She removes the desired portion of the wall by cutting through it in a gentle arch/smiley face pattern, extending that past the coronary band prolapse and down below the affected tissue. She slowly pulls the wall off, easing apart the coronary papillae and lamellae.
- After removing the portion of the wall, she checks the remaining wall to make certain no sharp edges remain.
- She evaluates the coronary and lamellar tissues for degree of compromise. Mild cases will have some edema or swelling, but when the lamellae are gently massaged they begin to bleed (indicating the circulation has returned). Cases with moderate damage have unhealthy-looking coronary and lamellar tissue and may require more aggressive treatments such as application of platelet-rich plasma. Cases with long-term or severe damage may have devitalized tissue at the coronary band or lamellae, and the affected portion of the coffin bone might be evident.
- Rucker cuts a piece of felt to the size and shape of the resected wall, soaks it in Betadine, and bandages it tightly over the defect to minimize swelling. The bandage is changed daily, and new areas of epithelialization (growth of cells over the resected area) should be evident within a week. The defect should begin to cornify (harden) within seven to 10 days and will eventually grow out as new hoof wall grows down from the coronary band.
- Aftercare, especially keeping the foot tightly bandaged, is critical, Rucker said, as is aggressively treating cases at the first sign of swelling or drainage from the coronary band.
Rehabilitating Chronically Laminitic Feet
How veterinarians and farriers manage the chronically laminitic foot can often determine whether that horse can live a useful, relatively pain-free life. Agne discussed how discussed how the Rood & Riddle podiatry team approaches such cases.
Agne first assesses the foot, noting whether the coffin bone is stable within the hoof. His treatment goals are to:
- Address the underlying cause;
- Reestablish vascular perfusion (healthy blood flow) to the dorsal solar corium (the inner tissues from which the sole grows) to encourage sole growth;
- Encourage healthy wall growth from the entire coronary band;
- Protect and unload lesions; and
- Treat any infections.
Agne recommended using radiographs to help farriers determine the proper trim for such horses. He said the type of shoe isn't as important as the proper trim and good therapeutic mechanics.
Generally, veterinarians and farriers will try to move the foot's base of support toward the heels (to reduce load on the toe), raise the heels (to reduce the pull of the deep digital flexor tendon on the coffin bone), and ease the foot's breakover toward the heels (also helping reduce load/torque on the toe). Support material can be used to help recruit the frog for partial weight bearing (thereby reducing weight on the wall).
For chronically laminitic horses that have toe cracks and/or poor-quality hoof wall, Agne has had success using hoof casts to stabilize the hoof capsule. After casting the foot, he adds the appropriate shoe. In these cases, he advises the horse owner to carefully monitor the heel bulbs just above the cast to be sure they don't get pinched or develop a lesion.
If a horse has severe rotation of the coffin bone, penetration or imminent penetration of the sole, and unrelenting pain that doesn't respond to therapeutic shoeing, Agne said a deep digital tendon tenotomy (cutting the deep digital flexor tendon that attaches on the bottom of the coffin bone) might be the only option to pursue with that horse.
"Case selection is really important," said Agne. "With a tenotomy, we're loading the back part of the foot." Horses that have a weak heel structure or show evidence of medial and/or lateral displacement of the coffin bone have a poorer prognosis than those that have robust heel structure and no evidence of coffin bone sinking.
Secondary complications of a tenotomy can include seromas (swelling due to localized collections of serum) in the sole or separated laminae, coronary band lesions as a result of coffin bone sinking, infections, flexor tendon contracture, and problems within the foot resulting from temporarily reduced stability of the coffin bone including navicular bone fractures and coffin joint subluxation. Thus, following up with correct derotation shoeing to properly support the foot is critical, Agne said, as well as closely monitoring the patient.
Applying Laminitis Research to Clinical Practice
Divers spoke about how veterinarians are putting the whole picture together to help treat and prevent laminitis cases. He explained three reasons why applying results of research to actual cases is difficult:
- Laminitis has several different causes, including EMS, systemic inflammatory disease (SID), Cushing's, corticosteroid use, and uneven weight-bearing.
- With SID, two different models are used in research to induce laminitis (carbohydrate overload and black walnut extract). Some differences exist in the pathophysiology of the disease in each model.
- There are different stages of laminitis, all with different pathophysiologic findings, making it more difficult to study disease mechanisms and target treatment.
In treating horses with conditions that could lead to laminitis, Divers has two goals: treating the primary disease and inhibiting the laminitis disease process in the hoof. He begins by treating the whole horse to control sepsis. He then works on the foot to prevent laminitis or provide treatment during the earliest stages.
Non-steroidal anti-inflammatory drug (NSAID) use is well-documented in alleviating many clinical signs associated with SID, but Divers said NSAID use is not as well-documented for efficacy in directly preventing laminitis.
One treatment that has been shown to work well to prevent laminitis in at-risk horses is cryotherapy (cold therapy). Lowering the temperature of the foot might decrease laminar inflammation by inhibiting destructive enzyme activity and oxidative reactions. It also decreases laminar metabolism, thus decreasing oxygen and nutrient requirements. Lastly, it might also decrease the delivery of blood-borne toxins that can trigger enzymatic destruction of the laminae.
Divers recommends that in conjunction with other therapies, veterinarians should employ cryotherapy to ice the feet of horses with systemic inflammation and endotoxemia for 24 hours past the point where the horse shows a normal heart rate, digital pulses, rectal temperature, and neutrophil morphology.
About the Author
Tracy Gantz is a freelance writer based in Southern California. She is the Southern California correspondent for The Blood-Horse and a regular contributor to Paint Horse Journal, Paint Racing News, and Appaloosa Journal.