Laminitis: What every horse owner should know
Clare Barfoot RNutr., SPILLERS® Research and Development Manager
Anyone that has owned or cared for a horse or pony that has suffered from laminitis will know how painful and debilitating the condition can be; it can even be fatal in some cases. Don’t be fooled into a false sense of security that laminitis only affects fat ponies; it can strike almost any horse or pony at any time. In managing the condition the focus should clearly lie with reducing the risk of it occurring.
What is laminitis?
Laminitis in its simplest sense is the inflammation of the laminae of the inner hoof wall (see diagram below) resulting in lameness. However, laminitis should not be thought of as a disease of the foot or hoof; it is merely expressed in the feet. Laminitis is a metabolic condition that affects the whole body and results from a complex cascade of events often starting in the digestive tract.
Why laminitis is important
Laminitis has plagued the horse since the beginning of recorded history. A disease of domestication laminitis can strike almost any horse or pony at any time irrespective of breed, age, body condition or environment from the stereotypical overweight pony to the racehorse in full training. However, the majority of affected animals seem to be ponies especially those at grass, with a greater prevalence during seasons of high grass growth eg. Spring and Autumn. Laminitis occurs worldwide across the whole equine industry. According to a general survey in America, apart from colic, laminitis is the most common reason a horse or pony will be presented for veterinary treatment. A large study in the UK in 1996 estimated that around 8,000 horses suffer from laminitis each year, around 600 have to be put down because of it and 1,300 animals are left permanently unsound.
Despite the huge welfare issues associated with laminitis vets and scientists still don’t fully understand the precise cause of this condition. However, researchers are getting closer to understanding the changes that occur in the hoof during the developmental stages of laminitis but there are still many unanswered questions.
Although treatment is extremely important, management is the key to reducing the incidence of the condition; much of the current research is therefore investigating potential trigger factors as well as the cascade of events that may culminate in laminitis. This research will hopefully enable laminitis prevention strategies to be targeted most effectively.
Causes of laminitis
• The most common cause of nutritionally induced laminitis is an overload of rapidly fermentable carbohydrate either from starch found in cereals and plants or sugars and fructans found in grass.
• The long term feeding of sugar and starch based feeds particularly to overweight ponies may lead to changes in glucose metabolism resulting in insulin resistance.
New thoughts- The role of insulin resistance
It has been well recognised that overweight horses especially ponies are more prone to laminitis; this may in part be linked with increased risk of concussion but is more likely to be associated with insulin resistance.
Insulin resistance is a component of several metabolic conditions and a risk factor for the development of many diseases in humans as well as the horse. In man these conditions include type II diabetes, obesity, coronary heart disease and cancer. In the horse changes in insulin sensitivity are associated with certain diseases, including some forms of tying up, developmental bone problems, hyperlipidemia and laminitis. Insulin resistance is regarded generally as a diminished ability of a given concentration of insulin to exert its normal effect therefore the body just has to keep releasing more and more insulin to elicit the same effect.
Obesity and diet have been shown to have an effect on insulin sensitivity. It has been suggested that the risk for laminitis in obese horses (condition score >7 on a 9 point scale) is more appropriately associated with the development of insulin resistance. Insulin sensitivity has also been shown to be lower in laminitic animals suggesting its role in the development of laminitis. The “syndrome” of obesity, insulin resistance and laminitis in mature horses has been referred to as either “peripheral Cushing’s syndrome” or an equine “metabolic syndrome”. Insulin sensitivity has also been found to be affected by diet; large fluctuations in glucose and insulin following meals high in sugar and starch (eg. cereals) may supply inappropriate signals of energy availability altering the insulin sensitivity of the tissue. The link between obesity, insulin sensitivity and blood flow to the foot in the horse is currently being investigated.
Potential non nutritional causes
• Concussion or mechanical trauma from a physical injury, excessive trotting on roads or jumping on hard ground. Overweight horses and ponies are perhaps more at risk due to the heavier weight loading to the feet.
• Chronic laminitis is one of the most obvious and hardest to manage symptoms of Cushing’s disease.
• Laminitis can also be caused by long term incorrect foot trimming, particularly if the heels are allowed to become too long, breaking the hoof pastern axis and putting excessive strain on the structures of the foot.
• Mares that fail to fully pass the placenta (cleansing) after foaling are at significant risk of endotoxaemia and toxin induced laminitis from an inflamed or infected uterus. Larger breeds of mare seem to be most commonly affected.
• Excessive weight bearing on one limb often seen following an injury to the opposite limb.
• Stress such as travelling and competing.
• Administration of some drugs such as corticosteroids in susceptible animals.
Picture of a pony showing a characteristic laminitic stance (courtesy of The Royal Veterinary College)
Reducing the incidence of laminitis is most effective if focused on management; according to an American veterinary report in 2000 50% of all laminitis cases could be prevented through appropriate nutrition.
• Condition score
Aim to maintain a moderate body condition score between 4 and 5 (moderate) out of 9. This will reduce the risk of nutritionally and mechanically induced laminitis and the development of insulin resistance which can contribute to the condition.
Weigh regularly ideally using a weighbridge or if unavailable use a weightape to monitor any changes in weight.
If weight gain becomes evident review the diet and consider restricting grazing and increasing the exercise.
Feeding strategy for reducing the risk of grain/starch induced laminitis
• Avoid cereals and high cereal concentrates such as coarse mixes. Many horses and ponies in light work don’t require supplementary feed, although vitamin and mineral requirements must be met.
• If supplementary feed is necessary in order to sustain animals in harder work choose feeds based on fibre and oil with low levels of sugar and starch. Look for feeds that have for example been approved by The Laminitis Trust.
• If required consider using oil as an energy source rather than starch (remember to add gradually, balance the overall diet and add additional vitamin E at 100-150iu/ 100mls of oil)
• If any cereals apart from oats are fed make sure they are processed by cooking (steam flaking, micronising, extruding or pelleting) to make the starch more easily digested, reducing the risk of starch overload.
• Feed fibre at a minimum quantity of 1% of bodyweight split between frequent meals, in many cases it may be more appropriate to feed fibre at closer to 2% of bodyweight.
• Make all dietary changes slowly.
• Keep meal sizes small (no more than 2.0kg per meal for a 500kg horse or less for lighter horses and ponies).
• Keep all feed room doors closed to reduce the risk of horses accidentally gorging on cereal based feeds.
Feeding strategy for reducing the risk of grass/fructan induced laminitis
Grass-induced laminitis is often thought of as a spring condition but this is a misconception; it is true that soluble carbohydrate levels will be highest when the grass is growing but grass in temperate climates grows for most of the year with a flush in spring and autumn. Grass therefore poses a significant risk for susceptible animals all year round.
It is impossible to predict the level of fructan in pasture at any given time therefore horses or ponies prone to laminitis should ideally be kept off pasture during the grass growing season (spring until flower development and autumn). However, if some grazing is inevitable following are some recommendations:
• Turn horses out to pasture late at night until early morning, removing them from pasture by mid-morning at the latest.
• Avoid pastures that have not been properly managed by regular grazing or cutting. Try to maintain a young sward. Mature stemmy pastures may contain high levels of fructan.
• Avoid/restrict turning out in spring (before flower development) and autumn when water soluble carbohydrate and fructan levels are likely to be highest.
• Restrict grass intake by using a grazing muzzle (that still allows drinking), grazing with sheep, turning out in a sparse paddock or by strip grazing. (Do not strip graze if a large quantity of grass is available). Turning out in an arena or woodchip surfaced area may also be beneficial.
• Do not turn horses out onto pasture that has been exposed to low temperatures in conjunction with bright sunlight e.g. sunny frosty mornings.
• Do not allow animals to graze on recently cut stubble such as after hay harvest.
• In known laminitics consider no grazing whilst providing a suitable forage.
• Choose mature forages such as late cut hay that are likely to be lower in water soluble carbohydrate (it is advisable to have your forage analysed and try to feed a forage with less than 10% water soluble carbohydrate). Alfalfa is also suitable as it is low in fructan but does contain starch so it is again advisable to have it analysed before feeding. Good hygienic straw, when appropriate, can also be mixed with hay to reduce its energy density.
Are there any dietary supplements that may help?
The first thing to say here is that there has been little if any controlled trials that have tested dietary supplements or feed additives or even dugs for that matter that work to prevent laminitis. Areas that could be explored include the role of increased antioxidant supplementation, the importance of additives that may stabilise pH in the hindgut and the role of agents that may help block the activation of MMP’s (enzymes that break down the lamellae bonds between the pedal bone and the hoof wall). However, perhaps currently one of the most important areas of interest is around those nutrients or nutraceuticals that might counter either the development of insulin resistance or the effects of being insulin resistant. Two such nutrients that are currently creating some interest are magnesium (which is essential for a horse in its own right) and the common spice cinnamon.
Cinnamon may be an unusual spice to feed to a horse but in human medicine there is increasing interest in this spice due to its beneficial effects on insulin sensitivity particularly in people suffering with type II diabetes. It is suggested that even at low doses cinnamon could have significant effects on fasting glucose concentrations. Although as yet no trials have been performed in horses cinnamon may prove to have benefits effects in laminitic ponies where insulin resistance may be underlying.
Again in human medicine there has been increasing interest in the potential role of magnesium in supporting the action of insulin. It has been suggested that in humans with type II diabetes with low magnesium status magnesium can improve insulin sensitivity. So what about horses- low magnesium status is often not reported in overweight horses or those predisposed to or suffering from laminitis also that doesn’t mean it doesn’t exist. Therefore more studies are needed to see if magnesium supplementation over and above the level normally provided in the diet does have any beneficial effect on insulin sensitivity and laminitis in the horse. Until then it would certainly seem appropriate to ensure that all horses have an adequate intake of magnesium.