Equine Cushing’s SyndromeThe existence of Equine Cushing’s Syndrome (ECS) has long been known. Most horse and pony owners associate it with an image of an elderly, very hairy horse, losing his coat late every year, with muscle wastage and being very susceptible to laminitis.

ECS is caused by excessive growth of cells in the Pars Intermedia of the Pituitary gland. Researchers still disagree whether this should be referred to as hyperplasia or a benign tumour however vets often refer to ECS as Pituitary Pars Intermedia Dysfunction (PPID). These cells do not respond to the normal feedback mechanisms signalled by the hypothalamus which leaves adrenocorticotrophic hormone (ACTH) production to continue unabated. It is this flow of ACTH which ultimately results in the many symptoms we see in affected elderly horses or ponies such as a very heavy coat, leading to excessive sweating; severe muscle wastage, particularly over the topline; bulges above the eyes; pot bellies; poor teeth; lethargy; chronic laminitis; susceptibility to infections and sometimes excessive drinking and urination. Many of these symptoms are initiated by the stimulating effect ACTH has on the adrenal glands, promoting cortisol production, for example cortisol promotes the catabolism of muscle.

In response to improved feeding and management horses and ponies are living to a greater age and we are seeing more cases of ECS in the UK. Estimates vary from 10% of horses over fifteen to a staggering 80% of horses/ponies over 18 years of age being affected to some degree.

Recent research looks at their relationship with LaminitisBy Nicola Tyler B.Sc. (Hons), Nutrition Director, TopSpec Equine

Cushings/IR/EMS®

IR and EMSAbout ten years ago we also started to see a huge rise in the number of horses/ponies which appeared to have some Cushing’s Syndrome-type symptoms but which were much too young according to the classical definition. It was not unusual to hear about ponies in particular, which were extremely good-doers and very prone to laminitis, often with wonderful coats. These cases started to be referred to as ‘Peripheral Cushing’s’ referring to the possibility that the dysfunction originated from the adrenal glands rather than the pituitary.

However recent research has started to define two ‘conditions’ which both affect younger (4-18 years old) horses and ponies and help to explain many previous mysteries. Chief amongst these was the fact that quite a significant group of laminitic horses and ponies either failed to respond sufficiently to potentially ‘curative’ changes in nutrition and management or relapsed despite continued correct feeding and management.

These two ‘conditions’ are termed ‘Insulin Resistant’ (IR) and ‘Equine Metabolic Syndrome’ (EMS). Neither term is ideal but they are what is currently being used.

The relationship between ECS, IR and EMSThe overlap and inter-relationship between ECS, IR and EMS is both complex and not yet fully understood but researchers around the world are having a fascinating time unravelling the confusion.

It has been known for many years that laminitis is rarely straightforward and that most cases are caused by more than one factor. For example a show horse may have been fed on a high-starch mix, be carrying a lot of weight and also have suffered some mechanical trauma to his feet when being lunged for long periods of time on uneven ground before going in the ring. However recent research has demonstrated that even more factors may be involved and also helps to explain why some horses and ponies do not respond to correct nutrition and management alone.

Nicola Tyler BSc (Hons)TopSpec Equine Limited Helpline 01845 565 030 nutritionist@topspec.com

• EquineCushing’sSyndromedevelopsinelderlyhorses when dopamine becomes increasingly unable to inhibit the production of ACTH, and other factors, from the pituitary. According to recent research the reduction in production of dopamine by the hypothalamus may be due to oxidative damage.

• ECS is rarely seen in horses less than ten years old.

• How many symptoms a horse shows varies a great deal and although if a hairy coat is combined with two or more of the symptoms above ECS is very likely, it is best to ask your vet to carry out one or more specific tests.

Current veterinary opinion is that the dynamic ‘low’ dexamethasone suppression test is best however if you are concerned about the very small risk of promoting laminitis then a lot can be learned initially from several repeated basal samples for glucose, insulin and ACTH. The problem with taking just one sample is that both glucose and insulin values can vary significantly despite attempts to sample in ideal nutritional and management circumstances. Most horses with ACTH values exceeding 50pg/ml will have ECS although both false positives and false negatives can occur. High glucose levels are rare but can be indicative of ECS because there is a high risk of secondary insulin resistance, however this does not always occur. High insulin levels will also indicate primary insulin resistance or secondary insulin resistance caused by a non-ECS condition. Laminitic horses cannot be meaningfully sampled for insulin or glucose because pain alone will cause raised levels. Ultimately it may be still be necessary to perform a dynamic test to secure an accurate diagnosis.

• Up to 85% of horses with ECS respond well to the reasonably-affordable drug Pergolide (stimulates dopamine production); others with good theoretical claims have been tried but have been less successful. No treatment can actually reverse the physical changes in the pituitary but Pergolide has been shown to reduce the levels of ACTH circulating in plasma. Consult your vet about what treatment might be appropriate for your horse or pony.

• Correct nutrition and management can add hugely to the quality of life of horses suffering from ECS. Hay should be selected that is late-cut from meadows and it, or any substitute forage fed when horses can no longer chew effectively, should contain less than 10% sugars and starch, often referred to as Non-Structural Carbohydrates (NSC) by the testing laboratory. Ideal chops are either TopChop Alfalfa or TopChop Lite depending on whether or not weight gain is needed.

Any ‘hard’ feed given should also be low in sugar and starch and ideally formulated without cereal grains, for example TopSpec CoolCondition Cubes or TopSpec FibrePlus cubes. An underweight horse suffering from ECS, with poor topline, but not currently laminitic should have his condition slowly and safely increased with the use of TopSpec Comprehensive Feed Balancer which contains good quality protein and generous anti-oxidant levels, unmolassed alfalfa chop for example TopChop Alfalfa, low-starch cubes, for example TopSpec CoolCondition Cubes and/or unmollassed sugar beet pulp. This hard feed part of the diet should also contain less than 10% NSC.

In the early stages of ECS many horses are overweight and very good-doers, these should be fed 1.5-2% of their bodyweight as hay (as described above) soaked in fresh, clean water for up to 12 hours to reduce its calorie content but leave the horse with plenty of essential fibre for hindgut function. As a hard feed these horses should receive either TopSpec Comprehensive Feed Balancer or simply a pelleted multi-supplement on its own, to provide vital micro-nutrients, for example TopSpec AntiLam. For all horses diagnosed with ECS grazing may need to be limited semi-permanently or permanently depending upon the circumstances, particularly susceptibility to laminitis.

• When monitoring the success of diet and management changes it is worth noting that horses that maintain an insulin level below 100 µU/ml have a better long-term prognosis than otherwise. With correct nutrition and management, if necessary backed-up by appropriate medication, most horses suffering from ECS can have a good quality of life for many years.

A thirty-year-old pony showing classic signs of Cushing’s Syndrome

• InsulinResistanceisnotanewconditionbutitisone that has attracted a great deal of research and discussion recently and is usually a major factor in what is now called Equine Metabolic Syndrome. Insulin is a hormone that responds to rising glucose levels in the blood by promoting the movement of glucose from the blood into cells to help maintain blood glucose levels within narrow boundaries. When cells become less sensitive or ‘resistant’ to the action of insulin blood glucose levels rise and serious consequences arise, not least an increased susceptibility to laminitis.

One trial showed that ponies at greatest risk of developing laminitis could be predicted from blood tests for glucose, insulin and triglycerides before laminitis developed. These ponies were classified as EMS by the researchers involved. Uneven fat distribution is classical with cresty necks (often with a dip in front of the withers) and fat pads behind the shoulder and on top of the quarters near the tail often seen.

• Most researchers feel that it is not necessarily helpful to try and distinguish between a horse that is merely IR and one that is suffering from EMS because the interrelationship of these conditions is complex and can also change due to many factors such as condition and season. However a horse may be viewed as suffering from EMS at the time of sampling if both insulin and ACTH levels are raised, whereas a horse may be considered IR if insulin is raised and ACTH is normal.

• IR in horses can be compared to Diabetes Type II in humans in many, but not all, ways.

• Some breeds or types of horses and ponies are genetically more likely to be Insulin Resistant, for example native ponies, especially the smaller breeds, Arabs and Quarter Horses.

A sixteen-year-old obese pony mare. An exceptionally good-doer, she is highly likely to be IR but has no signs of EMS and has never been

laminitic.

• Diet, age and body condition also contribute to the development of IR. However note that not all IR/EMS horses are overweight. In addition overweight horses may not be IR/EMS! Most, but not all, horses with ECS are IR. Good-doers are at a greater risk of IR. Horses fed high-sugar/starch diets are more likely to be IR than horses fed high-fibre and even high-fat diets whether they are in correct condition or overweight.

• The horse’s body can adapt to insulin resistance for some time by producing more insulin and keeping glucose levels under control, this is called ‘Compensated insulin resistance’. When high insulin levels fail to overcome cell resistance and blood glucose levels rise beyond normal parameters the term used is ‘Uncompensated insulin resistance’. Uncompensated insulin resistance usually occurs when IR has been going on for a long time and often indicates that ECS is present but note that pain and stress, in this case probably caused by laminitis, can cause increased blood glucose levels.

• Testing for IR can be carried out by measuring basal blood glucose and insulin levels as described under ECS and with all the same concerns. Levels of insulin in the blood exceeding 30 µU/ml indicate IR. Once again dynamic testing is considered superior and a combined glucose-insulin tolerance test is informative but its use is not always appropriate. Again, consult your vet.

• Correct nutrition and management can ensure long and productive lives for IR/EMS horses and ponies. The dietary advice given for horses suffering from ECS is equally appropriate here although far fewer IR horses are underweight. EMS horses can be! Ample exercise for sound horses is beneficial in increasing insulin sensitivity. Associated conditions such as laminitis will also respond to correct nutrition and management but may respond more fully if veterinary treatment is also applied.

• Although there is no clear biochemical logic in treating laminitis resulting from IR/EMS with Pergolide it not only has a high success rate but it may deter the development of ECS, and its success indicates once more that these syndromes are not yet fully understood.

Although IR and EMS lower a horse’s threshold for laminitis he need not necessarily suffer from it. If you can feed and manage your horse correctly you can prevent laminitis ever occurring. Feeding late-cut, tested low-sugar, meadow hay with a cereal-grain-free, low starch, top specification feed balancer i.e. TopSpec Comprehensive Feed Balancer to minimise hard feed requirements is the ideal starting point.

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Suitable products for nutritional support:

AntiLamTopSpec AntiLamA palatable and pelleted product including several supplements.

Designed for Good-Doers and those prone to laminitis. Very low calorie/high fibre formulaAvailable in 7.5 kg tubs and 20 kg sacks

Nicola Tyler BSc (Hons)TopSpec Equine Limited Helpline 01845 565030 nutritionist@topspec.com

Multiple winner forexcellence in nutritionaladvice and customer service2007 - 2008 - 2009 - 2010

TopChop LiteMade from high-temperature-dried British alfalfa and high quality chopped oat straw with added real mint to improve palatability. Very lightly dressed with soya oil so that alfalfa leaves can be included in the chop. Contains no molasses or any other sugar coating. Exceptionally low in sugar and startch (including fructans).

TopSpec AlfalfaPure high-temperature-dried British alfalfa with added real mint to improve palatability and lightly dressed with soya oil so that alfalfa leaves can be included in the chop. Contains no molasses or any other sugar coating. Very low in sugar and starch (including fructans) and contains no preservatives or artificial additives or colourings.

If extra calories are required then again, stick to low sugar/starch products such as unmolassed alfalfa chops e.g. TopChop Alfalfa and cereal-grain-free conditioning cubes i.e. TopSpec CoolCondition Cubes. This approach to feeding has many other benefits including

lowering the incidence of colic, D.O.D., ‘tying-up’ and is also ‘Non-Heating’. As there are no drawbacks to this approach it seems a tempting way to increase your horse’s chances of a healthy future.

TopSpec Comprehensive Feed BalancerTopSpec Comprehensive Feed Balancer is cereal-grain-free, palatable and

pelleted. It is a very flexible, nutrient-rich feed designed to balance the rations of most horses and ponies simply by adjusting the rate at which it is fed and the products it is fed with. It contains contains several supplements combined with

a feed designed to promote muscle development and function. A broad-spectrum supplement is backed up by others including a superb hoof supplement, generous

levels of anti-oxidants and sophisticated digestive aids.Available in 20 kg sacks.