Equine Cushing’s Disease/PPIDThe existence of Equine Cushing’s Disease 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.

ECD is caused by excessive growth of cells in the Pars Intermedia of the Pituitary gland; therefore vets prefer to refer to it as Pituitary Pars Intermedia Dysfunction (PPID). The enlarged pituitary produces excessive adrenocorticotrophic hormone (ACTH). 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 or poor performance; chronic laminitis in over 50% of cases; susceptibility to infections and, in about 30% of cases, excessive drinking and urination. Persistent lactation may also occur.

In response to improved feeding and management horses and ponies are living to a greater age and we are seeing more cases of PPID reported 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.

EMSAbout fifteen years ago we also started to see a rise in the number of horses/ponies which appeared to have some PPID-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 mistaken possibility that the dysfunction originated from the adrenal glands rather than the pituitary.

Recent research tries to unravel their relationship with each other and with LaminitisBy Nicola Tyler BSc (Hons), Nutrition Director, TopSpec Equine

CUSHINGS (PPID) and EMS/IR

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However recent research has started to define a ‘condition’ which affects younger (4-15 years old) horses and ponies and help to explain many previous mysteries. This condition is termed ‘Equine Metabolic Syndrome’ (EMS), however many vets simply refer to the main hormonal dysfunction that occurs in horses and ponies with EMS, that is insulin resistance or IR.

The relationship between PPID and EMS/IRThe relationship between PPID and EMS/IR is both complex and not yet fully understood but researchers around the world are having a fascinating time unravelling the confusion. In the UK Andy Durham, from Liphook, has noted some interesting differences in these relationships between horses and ponies.

• More PPID cases were seen in ponies (61%) than horses (39%).

• PPID horses were significantly older than PPID ponies seen.

• IR was more common in PPID ponies (49%) than PPID horses (36%).

• High levels of triglycerides (constituents of fat) in the blood were more common in PPID ponies (53%) than PPID horses (28%).

• Higher ACTH levels in horses were associated with increased age.

The data collected appeared to show that in horses PPID can cause IR. However in ponies this appears unlikely, conversely they may often be IR at the onset of PPID but subsequent weight loss as a result of PPID gradually improves insulin sensitivity. Laminitis is more likely to occur in PPID horses and ponies if they are also IR.

It has been known for many years that laminitis is rarely straightforward and that most cases are caused by more than one factor. However recent research around the globe has demonstrated that even more factors may be involved and has focussed on hormonal (endocrinopathic) causes of laminitis, particularly Insulin Resistance and Equine Cushing’s Disease. Whether horses and ponies with IR are more likely to develop PPID, or to develop it sooner, than horses and ponies with normal insulin sensitivity is a burning question.

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

PPID• PPID develops in elderly horses when reduced levels of

dopamine from the hypothalamus 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 local oxidative damage. The pituitary gland of horses with PPID contains only 10% of the dopamine in healthy horses.

• PPID 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 described earlier PPID 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 blood samples for glucose, insulin, triglycerides and, most importantly, ACTH. These should be taken after a short fasting interval. 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.

In the past it was thought misleading to test horses for ACTH in the autumn but Andy Durham from Liphook feels this is a good time to sample provided seasonally adjusted reference figures are used. Most horses with ACTH values exceeding 29pg/ml during November to July or 47pg/ml during August to October will have PPID, although both false positives and false negatives can occur.

High glucose levels are rare but can be indicative of PPID 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-PPID condition.

Horses suffering from laminitis 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 PPID respond well to the reasonably-affordable drug Prascend (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 PPID. Maintaining correct body condition is an important goal. 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).

Ideal chops are unmolassed and contain less than 10% sugar and starch, such as 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. An underweight horse suffering from PPID, 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. Plus 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 PPID 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 ample, fresh, clean water for up to 12 hours to reduce its sugar, starch and calorie content but leave the horse with plenty of essential fibre for hindgut function.

As a hard feed these horses should receive either a powdered multi-supplement e.g. TopSpec All-in-One mixed with dampened TopChop Lite or, if palatability is an issue, a pelleted multi-supplement e.g. TopSpec AntiLam on its own, to provide vital micro-nutrients. Avoid fat supplementation as this may worsen any insulin resistance.

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

For all horses diagnosed with PPID grazing may need to be limited semi-permanently or permanently depending upon the circumstances, particularly susceptibility to laminitis. For those with concurrent IR, seasonal restriction in Spring and Autumn is recommended.

When monitoring the success of diet and management changes it is worth noting that horses that maintain an insulin level below 50 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 PPID can have a good quality of life for many years.

EMS/IR• Insulin Resistance is not a new condition but it is one that

has attracted a great deal of research and discussion recently and is usually the major hormonal disturbance 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. Recent research has shown that administering insulin to horses directly causes laminitis.

One trial showed that ponies at the 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. Fat can also accumulate in the sheath or around the mammary gland. Nonetheless ribs can frequently be seen and may look sprung. Most horses and ponies that are I.R. are good-doers, sometimes exceptionally so.

A sixteen year old, obese, pony mare. An exceptionally good-doer, she is likely to be predisposed to IR but has no signs of

EMS and has never been laminitic.

• IR in horses can be compared to Diabetes Type II in humans in many, but not all, ways. However IR rarely develops into true diabetes in horses or ponies.

• Some breeds or types of horses and ponies are genetically more likely to be IR; they are good-doers, for example native ponies, especially the smaller breeds, Arabs, Cobs, Spanish and Quarter Horses. Horses and ponies that evolved in harsh climates on native grass species often gain weight easily when fed on UK pastures improved for cattle or good forage; this may well explain why they are prone to EMS.

• Diet, age and body condition also contribute to the development of IR. However note that not all EMS/IR horses are overweight. In addition overweight horses may not be IR, although dynamic testing usually demonstrates that they are. 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.

• Testing for IR can be carried out by measuring basal blood glucose and insulin levels, after a short period of fasting, as described under PPID 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 and may be needed to confirm diagnosis. Again, consult your vet.

• Correct nutrition and management can ensure long and productive lives for EMS horses and ponies. The dietary advice given for horses suffering from PPID is equally appropriate here although fewer EMS/IR horses are underweight. Ample exercise for sound horses is beneficial in increasing insulin sensitivity. When horses and ponies are not sound but need to lose weight to lower their insulin resistance, vets may prescribe a short course of Metformin, usually for three months only. Metformin should in theory increase insulin sensitivity in equine peripheral tissues but results have been mixed, possibly because of poor absorption through the digestive tract. The ideal dosage for horses is still being fine-tuned. 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 obvious biochemical logic in treating laminitis resulting from EMS/IR with Prascend it can be successful and it may deter the development of PPID, and its success indicates once more that these syndromes have complex inter-relationships.

• Although EMS/IR lowers 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. Aim for slightly below ideal body weight. Restrict or eliminate grazing, especially during Spring and Autumn. Feeding late-cut, tested low-sugar, meadow hay with either a powdered multi-supplement i.e. TopSpec All-in-One multi-supplement mixed with a little TopChop Lite or, if palatability is an issue, a pelleted multi-supplement i.e. TopSpec AntiLam (if he is overweight) or a cereal-grain-free, low starch, top specification feed balancer i.e. TopSpec Comprehensive Feed Balancer (if he is underweight) to

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Suitable products for nutritional support:

AntiLamTopSpec AntiLamA palatable and pelleted product including a multi-supplement. Designed for Good-Doers and those prone to laminitis. Contains 5-way nutritional support for horses and ponies, prone to, being treated for and recovering

from laminitis. Very low calorie/high fibre formula.Available in 7.5kg tubs and 20kg sacks

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

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 starch (including fructans).Available in 15kg sacks

minimise hard feed requirements, is the ideal starting point.

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 low sugar/low starch approach to feeding has many other benefits including lowering the incidence of colic, stereotypical behaviour, 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 BalancerA 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 TopSpec All-in-One with a feed designed to promote muscle development and function. Cereal-grain-free, palatable and pelleted. Available in 20kg sacks

TopSpec All-in-OneThe most fully comprehensive supplement you can buy and it can successfully be fed to every

horse or pony on your yard. It includes a broad-spectrum supplement plus many specialised supplements including a hoof supplement, anti-oxidants and digestive aids.

Available in 4kg, 9kg and 20kg tubs