What is Cushing's syndrome or Pituitary Pars Intermedia Dysfunction (PPID)?
Cushing's or more correctly, PPID (Pituitary Pars Intermedia Dysfunction), is an endocrine or ‘hormonal’ disorder involving the pituitary gland. In affected horses and ponies the pars intermedia or ‘middle lobe’ becomes over active (and often enlarged) and produces large amounts of several hormones including adrenocorticotropin hormone or ‘ACTH’. How this rise in hormones leads to clinical signs of PPID is not yet understood.
Who is at risk?
PPID is most commonly diagnosed in older ponies although horses and younger animals can also be affected. There does not seem to be a breed or sex bias and in fact, it has been suggested that ponies may be more commonly affected simply because they tend to live longer.
What to look out for
If you suspect your horse or pony may have Cushing's it is important to get a confirmed veterinary diagnosis. Signs of Cushing's syndrome include:
- Failure or later shedding of the winter coat that may become really long, matted and curly especially around the legs.
- Excessive sweating.
- Increased drinking and urination.
- Lethargy and poor performance.
- A pot-bellied appearance.
- Loss of muscle and topline.
- Abnormal fat distribution particularly above the eyes, the crest of the neck and above the tail head.
- Chronic or relapsing laminitis.
- Delayed wound healing, increase in infections of the skin and susceptibility to internal parasites.
How nutrition plays a role
Although there is no cure for PPID, with careful management, appropriate nutrition and veterinary treatment, many horses and ponies continue to have comfortable and active lives for a number of years. Nutritional management of horses and ponies with PPID is very similar to that of a laminitic and should therefore focus on maintaining a healthy body condition score (BCS) and providing a diet that is high in fibre and low in non-structural carbohydrate (NSC). Put simply, NSC is the sum of starch, sugars and fructan, the storage form of sugar in grass and other plants.
Feed and management tips
- Balancers provide a concentrated source of vitamins, minerals and quality protein but due to the low feeding rate, contribute very limited amounts of calories, starch and sugar to the total diet, making them ideal for good doers.
- If additional calories are needed, look for fibre based feeds that are low in starch and sugar and if necessary, high in oil (oil is high in calories but starch and sugar free).
- Avoid mixes and other cereal based feeds (cereals are high in starch).
- Feed small meals. A maximum of 2kg per meal for horses, less for ponies.
- Although not scientifically proven, additional antioxidants such as vitamins E and C may be helpful. Speak to a nutritionist for more advice.
- Ideally suitable forage or a forage replacer should be fed ad lib.
- Total forage intake should not be restricted to less than 1.5% of bodyweight (dry matter). On average, this equates to approximately 9kg (11kg if you intend to soak it) for a 500kg horse without access to grazing.
- Ideally feed a low WSC hay or hay replacer low in starch and sugar. Although soaking hay helps to reduce WSC, results are highly variable and can’t guarantee suitability for laminitics. Due to a loss of nutrients into the water (and therefore dry matter), your haynet will also contain less ‘hay’ and more water post soaking. As a guide, increase the amount you soak by 20%.
- Aim to maintain a BCS of 4.5-5 out of 9.
- Make all changes in diet gradually, including changes in forage.
- Maintain a regular exercise programme where possible.
- Grass can continue to grow for most of the year but grows more rapidly in spring and autumn and therefore extra care should be taken during these periods.
- Restrict or remove grazing. For horses and ponies at very high risk of laminitis, complete removal from grazing may be the only option.
- Methods of restricting grass intake include using a grazing muzzle, strip grazing, turning out on sparse paddocks or ‘non-grass turnout’.
- Beware of binge eating! Turning out for short periods without a muzzle or allowing free access to grazing after removing a grazing muzzle can lead to gorging.
- Avoid turning out on sunny, frosty mornings. Grass exposed to cold temperatures in combination with bright sunlight may contain high levels of WSC.
- Consider turning out at night when WSC levels are likely to lower. Grass can’t photosythesise (and therefore produce sugar) without sunlight and provided it is warm enough, fructan will be used for growth overnight.
- Avoid pastures that have not been properly managed. Mature ‘stemmy’ pastures and grass that has been stressed by drought or over-grazing may be deceptively high in WSC.