A LOOK AT LAMINITIS AND EQUINE METABOLIC SYNDROME.
Laminitis has long been known as a crippling and depressing syndrome – Day and Sons in their book of “Every Day Farriery” in September 1885 describe laminitis as… “An extremely painful heated and inflamed condition of the foot”. The line drawing of a case in their book holds true of what we see today!
Acute Laminitis – Old and New!
For many years we have known that the syndrome in older horses known as Cushing’s syndrome is a predisposing factor to laminitic cases but in recent years there has been research into another syndrome that results in a high incidence of laminitis bouts – Equine Metabolic Syndrome. In reality there is probably considerable overlap between these two syndromes. One recent study has suggested that 9/10 horses with laminitis have an endocrine (hormonal) involvement. There are also other causes of laminitis – severe endotoxaemia, colic, retained placenta and weight bearing laminitis.
Equine Metabolic Syndrome (EMS).
EMS has also been known as peripheral or pseudo Cushing’s syndrome and Insulin Resistance Syndrome. Hypothyroidism has also been implicated in the past.
EMS is a term that is used to describe horses presenting with obesity and /or large regional fat deposits, insulin resistance and recurrent laminitis. Classically these horses are “good doers” gain weight on very little food intake and “live on the smell of an oily rag”! There seems to be an association with this type of horse and recurrent bouts of laminitis – the link and pathogenesis is not (yet) fully understood but is probably hormone based. One recent study in the UK revealed that 83% of horses presenting with laminitis were overweight. There seems to be a similarity to the condition known as “Metabolic Syndrome” in humans – where there has been in recent years an increased incidence of obesity in the Western World. Both horses and people suffering from this condition have insulin resistance and high glucose. Heart disease and high blood pressure are significant consequences in people whereas laminitis is the significant issue in horses.
What does an EMS horse look like?
EMS usually affects young to middle aged horses – usually 5 to 15 years of age, those that are older are more likely to have Cushing’s disease involvement. It is more common in native pony – type breeds, Arabians, Morgans, Quarterhorses, Miniatures and Haflingers but can also be seen in other breeds.
An EMS horse puts on weight easily and deposits fat in certain regions, these include the crest of neck (cresty neck), above the eyes, the shoulders, the tail base, around the mammary glands in the mare and around and within the sheath of geldings. Nature causes this type of horse to store fat when food is plenty in the summer and use up these fat stores in the winter when food is short.
An EMS Horse.
EMS horses may also have a pot bellied appearance and can present with excessive drinking and urinating (although this is not always the case). Broodmares with EMS can be difficult to get in foal and stallions may have fertility issues.
EMS horses also have a predisposition to lipomas associated with the intestines – these fatty lumps can wrap themselves around bowel and strangulate the blood supply therefore causing severe colic requiring surgery.
There may also be signs of recurrent laminitic episodes such as the characteristic growth rings on the hoof wall, dropped sole and white line separation. There may be a history of overt laminitic episodes or sometimes a mild recurrent lameness / pottery gait.
. Growth Rings.
What is the cause?
The combined effects of inappropriate diet, improved pasture, lack of exercise and a genetic predisposition to obesity in some individuals seem to be major factors in the development of EMS.
The precise pathogenesis is not fully understood but is it believed that the fat accumulation (adipose tissue) may have the ability to produce hormones (adipokines), inflammatory mediators, corticosteroids and enzymes that have metabolic effects within the body. It is possible that these chemicals may have the ability to down regulate the sensitivity of tissues to insulin – thus they become “Insulin Resistant” (IR). The excess inflammatory mediators also lead to a constant state of low grade inflammation.
What is Insulin Resistance?
Insulin is a hormone produced by the pancreas in response to high blood glucose and is an important regulator of food intake and energy balance. It maintains blood glucose within a strict range by stimulating uptake by muscle, fat and liver from the blood stream.
Insulin resistance is where tissues are unable to respond to insulin. As a result the blood glucose remains high and more insulin production occurs. The effectiveness of insulin on its target tissues is also interfered with by corticosteroids, free fatty acids and the adipokines described above.
How Is Insulin resistance involved in the development of laminitis?
The effects of high glucose in the horse seem to lead to recurrent laminitis bouts. Why? As yet we do not know! There are various research projects and teams across the world trying to ascertain why, including Professor Chris Pollit at the University of Queensland.
Possible causative factors include the effects of high glucose on blood pressure, the haemostatic properties of blood vessels and hence blood flow/ perfusion. There may also be an effect of high glucose in the foot at the level of the laminae – this layer contains the highly specialised cells that maintain the hoof integrity and have a very intricate network of blood vessels.
Intricate Network of Foot Blood Vessels.
EMS should be suspected in horses with the classical appearance described above. It should definitely be considered in cases of chronic or recurrent laminitis. It can however be a diagnostic challenge.
Simple laboratory testing is not always straight forward because there are multiple factors that can impact insulin and glucose levels in the horse – these include naturally fluctuating hormone levels during the day, time of year / season, stress, diet and when the horse was last fed etc. Sample handling and storage may also have some influence on the glucose. Also some horses with EMS may have normal levels of insulin and glucose. This may be because it is too early in the disease process for the levels to be changed. Hence a simple result does not always occur and the diagnosis may strongly suspect on appearance and laminitic history.
A simple screen can be performed by sampling blood for glucose and insulin, ideally this is performed after fasting the horse for 12 hours. Sometimes multiple sampling over a 24 period is advisable to see the pattern that occurs.
Horses that are suspect EMS cases but have normal levels should undergo “dynamic testing” – this maybe either a Combined Glucose Insulin Tolerance Test (CGITT) where both glucose and insulin are administered intravenously – the levels are then monitored over the next several hours to determine the response to administration. Another test that may be used is an oral glucose tolerance test. Both of these are usually performed in a hospital environment because of the repeat sampling over a period of time.
If Cushing’s syndrome is considered then an overnight dexamethasone suppression test or an ACTH Stimulation test may also be considered.
PREVENTION and TREATMENT.
Too many horses eat too many groceries!
Horses diagnosed with EMS should not be given grain, grain mixes with molasses or unlimited access to pasture. Ideally horse should be maintained on forage based diet preferably good quality grass hay (low sugar /low starch). Sugar content for hay for EMS cases should be 10 -12% or less. If the sugar content is suspected or known to be higher than the hay can be soaked for an hour then hung up to dry – this removes some of the soluble sugar. A complete vitamin and mineral supplement can be added. Feed should be little and often – consider the use of slow feeder systems such as small holed hay bags. If extra fibre is required use extruded beet pulp without molasses (e.g. Speedibeet – recommended by the Laminitis Trust) or if extra energy is required use non-starch alternatives such as rice bran. Your veterinary surgeon / nutritionist can help you work out a feeding plan for your EMS horse.
With regard to pasture – avoid lush pasture or the fresh growth after rain. Grazing muzzles have been shown to be effective in reducing pasture intake and still allow the horse to exercise. The muzzling seems to be better than turning them into a confined bald patch of ground. The worst time for turnout has been shown to be from mid morning to afternoon – there is some evidence to suggest that the frusta sugars are at their highest at this time. Although there does seem to be some controversy on this and whether the fructans are solely responsible for laminitic attacks! Stressed grasses after frost or floods should be avoided too.
Grazing Muzzle (e.g. “Best Friend“ muzzle.)
Starving is also not advisable as it leads to other issues such as hyperlipaemia, gastric ulcers and behavioural issues. Remember any dietary changes need to be made slowly to help in the prevention of colic.
Exercise is absolutely vital (as long as your horse does not have laminitis – your vet and farrier will guide you on this). Exercise has been shown to increase the uptake of glucose by muscles and thus reduce blood sugar levels. Exercise should be daily or near daily in the form of walking, lunging, driving or riding (or any combination). Obviously exercise should be introduced according to the horse’s level of fitness, age and soundness! Your vet will be able to advise you!
There are no specific medications suitable for treating EMS alone. Many of the medications tried are human drugs and seem to have a different effect and absorption in the horse. The use of pergolide or cyproheptadine may be used and are effective in Cushing’s cases but have been shown to be ineffective in EMS cases. Trilostane has been shown to be useful in some cases. Metformin (a hypoglycaemic drug used in people) has significant use in the UK but research has shown that it is probably not as effective in the horse due to a lack of absorption.
Your veterinary surgeon will determine whether any of these are suitable for your individual case as there are many factors to take into consideration.
ALTERNATIVE and Supplementary Therapies.
There is much interest in both the human and equine field. Often there is limited research. Some therapies that have been tried and maybe used are:
Chinese Cinnamon – stimulates glucose uptake. Effect unknown in the horse.
Hoof Amino Acid Supplements (e.g. KER Biobloom or Farrier’s Formula) – particularly biotin, methionine, lysine and chelated zinc. These have been shown to be beneficial for healthy hoof growth and aiding recovery from hoof issues such as laminitis.
Encapsulated Bicarbonate (e.g. KER Equishure) – this has been shown to help maintain the pH of the hindgut thus preventing acidosis. Hindgut acidosis occurs when there is overconsumption of high starch concentrates or from pasture rich in fructans. The acidosis occurs as a result in a change in the bacterial population of the hindgut and maybe associated with the development of laminitis.
Vitamin E – as an antioxidant, plays a role in immune, cardiovascular, circulatory, neuromuscular and reproductive functions. Horses may require supplementation when removed from pasture.
Magnesium and Chromium – limited studies but much anecdotal use! Some products available for the horse containing these as a supplement e.g. John Konke’s Trim. Research being performed may show effect – one to watch?!
Your veterinary surgeon will discuss if any of these maybe beneficial in your case.
EMS has in recent years been recognised as a problem. There is currently much research on this condition in both people and animals; hopefully more preventative and treatment strategies will come to light from this.
The key at this stage is recognising the type of horses that may have the potential to develop EMS or that actually have it and to instigate management strategies with diet and exercise to control it and to prevent bouts of laminitis.
Please contact Samford Valley Veterinary Hospital Large Animal Veterinarians if you or your hoof care provider thinks your horse may have EMS.
Paula Williams BSc (Hons) BVSc MRCVS