Laminitis

Laminitis, also referred to as founder, is a complex and serious disease that every horse owner should be aware of. It can occur in horses and ponies of any size, breed, or discipline, and unfortunately can mean the end of your horse’s career, or even their life.

The Normal Equine Foot

To understand laminitis you must first understand the normal anatomy of the equine foot. Encased by the hoof is the pedal bone, also referred to as the 3rd phalanx or coffin bone. On the surface of the pedal bone and on the inside of the hoof capsule are soft tissue sheets of lamellae which are finger like projections that interdigitate. These lamellae are responsible for literally suspending the pedal bone in place, resisting the huge amount of weight placed upon the pedal bone from the large body above. The hoof wall grows down from the coronary band and as new hoof grows the lamellae detach and reattach allowing the hoof wall to slide down over the pedal bone. The mechanism by which the body controls this detachment and reattachment is still not fully understood. Another important force the lamellae counter-act is the constant pull from the deep digital flexor tendon (DDFT) which inserts on the back of the pedal bone. This essentially tries to pull and rotate the pedal bone away from the front of the hoof.

What is Laminitis?

Laminitis is inflammation and swelling of the sensitive lamellae with failure of this delicate suspensory system. The lamellae and pedal bone can be affected in several ways.

Initially the lamellae are inflamed causing an increase in the distance between the hoof wall and the pedal bone. As this progresses and the delicate bonds are broken the pedal bone can rotate downwards away from the front of the hoof wall, under the influence of the DDFT. Eventually the pedal bone can rotate to such a degree that it can even penetrate the sole. The failure of lamellae can also allow the pedal bone to sink vertically towards the ground under the influence of the horse’s heavy body weight. The blood supply surrounding the pedal bone can consequently be affected due to the crushing forces of the pedal bone and inflammation. Any of these changes are extremely painful.

Clinical Signs

The degree of lameness a horse shows will depend on the severity of the laminitis and the number of feet affected. Laminitis can affect anywhere from one to four feet. Typically laminitis is seen in the forelimbs, presumably due to the fact that they carry more weight. Lameness is normally evident at the walk with a short shuffling stride. When standing the horse may shift their body weight from one leg to another, and when asked to lift up a foot they may be reluctant or even refuse due to the pain of putting all their weight on the opposite foot. They can also be reluctant to turn or back up and may spend more time lying down than usual.

Other signs include increased digital pulses, heat associated with the foot, and sometimes swelling of the legs. As the pedal bone rotates it puts pressure on the sole and this causes pain at the toe in front of the frog. A pain response may be elicited when hoof testers are applied over this area, or a response may even be seen with just digital pressure. As the pedal bone pushes further downwards a bulge and bruised area may be seen at this location, and eventually the pedal bone may completely penetrate the sole. Hoof wall changes can be seen as rings and depressions as the new hoof grows down. Laminitis can also affect the rate of growth of the hoof causing the front of the hoof to grow slower than the heels. A most spectacular example of this is when horses develop ‘Aladdins Slippers’.

Diagnosis

Based on clinical signs a preliminary diagnosis of laminitis can be made, however to confirm the diagnosis radiographs of all four feet are essential. The radiographs will indicate the potential severity of the laminitis and affect the course of treatment. Your vet can measure the distance between the surface of the hoof and the surface of the pedal bone, the degree of rotation of the pedal bone away from the hoof wall, and the distance that the pedal bone has ‘sunk’. The cause and chronicity of the laminitis can affect the severity and changes seen.

In severe cases another technique may be used where the veins of the foot are injected with radio-opaque liquid so that blood flow surrounding the pedal bone can be assessed on radiographs. This is referred to as a ‘venogram’.

Causes

There are a number of factors that can work independently or together to cause laminitis in your horse. Unfortunately the exact mechanisms that result in laminitis are still poorly understood and hotly debated.

Endotoxaemia Any infection or disease that causes endotoxins and inflammatory mediators to be released into circulation can cause laminitis. Prime examples of these are mares with retained placentas, some types of colic, colitis (diarrhoea), or pleuropneumonia, to name just a few. In these cases it is vital for your veterinarian to intervene immediately to treat the primary cause and to hopefully minimise the risk of laminitis.

Supporting Limb Laminitis If your horse injures themselves severely enough that they no longer bear weight on a leg, for example with a fracture or septic joint, it means that all of the weight is bore by the supporting limb. This effectively crushes the blood supply to that foot and causes laminitis. There is no rule as to how long it takes for supporting limb laminitis to develop, meaning that any severe lameness should be seen by your veterinarian immediately.

Grain Overload & Rich Pastures A common cause of laminitis pertains to diet. Laminitis can arise when horses gorge themselves on a large amount of concentrate feed, such as when horses accidently gain access to feed sheds. This delivers a huge amount of carbohydrates to the hindgut which, when digested by bacteria, causes the production of volatile fatty acids and lactic acid. This causes the pH to drop, further supporting these bacteria whilst causing the death of gram negative bacteria. It is thought that the death of these gram negative bacteria causes endotoxin release and thus laminitis.

Grass contains a sugar called fructan which when digested in the hindgut also produces

lactic acid. This is why laminitis may be seen when ponies are let into a lush paddock full of grass. Unfortunately the fructan content of grass cannot be determined by simply looking at the grass, with evidence that dry long stalk winter grass can just as easily have high fructan levels.

Fortunately not all horses are as sensitive to the production of lactic acid and a lowered pH in the hindgut which explains why a large proportion of horses are fed on lush pastures and high carbohydrate diets without concern.

Insulin Resistance There has recently been a link to insulin resistance and laminitis. Insulin resistance can be a problem in overweight horses, horses with Cushings Disease (pituitary pars intermedia dysfunction), and horses with Equine Metabolic Syndrome. Ponies are especially susceptible to becoming overweight, and therefore laminitic. Appropriate weight management of your horse cannot be stressed enough so please consult with your veterinarian if your horse is overweight to plan a healthy weight loss regime.

Corticosteroids Injections of corticosteroids, such as dexamethasone and triamcinolone, have been anecdotally linked with laminitis. Steroids should only ever be administered when necessary by a veterinarian.

Treatment

The lack of understanding as to how laminitis occurs means that as yet there is no true cure, but rather various techniques to help treat the symptoms and minimise the severity of the disease. The intensity of treatment your horse receives will depend on the cause, severity, and chronicity of the laminitis. In cases where there is a known event that has caused the laminitis, such as endotoxaemia, the primary disease must be treated immediately.

An essential component in any laminitis treatment regime is anti-inflammatories and analgesics. Non-steroidal anti-inflammatories such as Phenylbutazone (Bute) are most commonly used.

The amount of confinement required will vary depending on severity, but typically confinement to a stable with deep soft bedding is recommended during the acute stage of laminitis. Exercise is contra-indicated in horses with laminitis as this will further break the delicate bonds between lamellae.

You cannot manage your laminitic horse without the help of your farrier. With the aide of radiographs your farrier will aim to improve your horse’s comfort and try to counteract the forces at play on your horses pedal bone. This will involve removing any excess toe, and ideally applying a heart bar shoe which reduces the weight held by the sole and redistributes it to the walls and frog. Heel supports are added to help relieve some of the tension on the DDFT.

Dietary modifications are also essential.

In severe cases the DDFT can be cut to release the tension on the back of the pedal bone. This is very much a last resort, with no guarantee that horses will be comfortable in the paddock

despite this drastic measure.

In cases where endotoxaemia occurs a preventative measure can be taken to drastically reduce the risk of your horse developing laminitis. This involves cooling of the horses feet in an ice bath. Horses naturally have vascular shunts in their legs so that if standing in snow, for example, the blood may be shunted past the foot avoiding the freezing temperatures. The ice bath utilises this natural anatomy to minimise the blood flowing to the foot and therefore reducing the amount of harmful endotoxins and inflammatory mediators that reach the foot. This technique has been successfully used to prevent laminitis in endotoxic horses.

The aim of any treatment is to make the horse as comfortable as possible and support the hoof so that as new hoof grows from the coronet it maintains correct lamellae attachments. The hoof wall grows approximately 7mm a month, so it does take time and dedication before you have a ‘normal’ foot. In reality, a large number of horses are not able to kept comfortable and euthanasia is unfortunately the only humane option.

Prevention

Unfortunately once your horse has had laminitis they are almost always at a higher risk of developing it again. If you identify your horse as being at an increased risk of developing laminitis, for example an overweight pony, there are preventative measures that should be taken.

There are two key components to the prevention of laminitis: appropriate foot care and diet. It is essential for your horse’s feet to be regularly attended by a farrier, i.e. every 4-8 weeks. This prevents excessive toe growth which acts as a lever trying to pull apart the delicate lamellae bonds. They may also be able to alert you to the early stages of laminitis.

Essentially we want to restrict the amount of carbohydrates and fructans in the food we feed at risk or recovering laminitic horses, whilst still providing adequate fibre in the diet. In most preventative cases we are aiming to help the horse lose weight. It is essential that the horse is not starved to try and achieve weight loss as this can lead to other life threatening conditions. Rather the diet should be restricted to achieve weight loss slowly. Your veterinarian can help plan a weight loss program given your horse’s condition and living arrangements. Some helpful tips are to minimise grazing time on grasses which may be high in fructans. It is impossible to know which grasses are high in fructans so this can translate to your horse having limited access to pasture, or being kept only in a paddock that is regularly mown or recently grazed down by other horses. Equine muzzles are also available which still allow the horse to drink and graze but at a slower rate.

If hay needs to be given it is best to soak the hay in a bucket of water for an hour and then drip dry to allow soluble sugars to leach out of the hay. This is particularly advisable for lucerne hay which can be high in fructans and carbohydrates.

But what about if you have an underweight horse that has a history of laminitis? Your horse can still be given a mixed feed, the key is what you give. The Laminitis Trust in England has approved several feeds for laminitic horses. These include Hygain Ice, Happy Hooves, and Speedi-beet. These feeds carry the ‘Laminitis Trust Approval Mark’ on their packaging so ensure whatever feed you buy carries this logo.

There are also feed supplements that can be added to your horses feed to help reduce the risk of laminitis in high risk horses. FounderGuard is a product containing virginiamycin which is an antibiotic that helps control the population of bacteria responsible for lactic acid production in the hind gut. This is a prophylactic, meaning that the horse needs to have been eating this before it eats a large amount of grain or pasture high in fructans. Another product called Equishure is a hindgut buffer which helps to reduce pH and also supports the growth of lactic-acid utilising bacteria.

Exercise can not only help prevent or treat obesity but also to help reduce insulin resistance. Regular exercise is recommended for at risk horses that do not yet have laminitis.

Conclusion

Laminitis can be an overwhelming disease in its complexity and severity. This article’s aim is to help inform horse owners of some of the risks of laminitis and ways it can hopefully be avoided. This should not be used in lieu of veterinary attention, and if you suspect your horse may be suffering from laminitis or be at high risk please contact your veterinarian.