What is Cushing's syndrome or Pituitary Pars Intermedia Dysfunction (PPID)?
Cushing's or more correctly, PPID, is an endocrine (hormonal) disorder involving the pituitary gland. In non Cushingoid horses and ponies dopamine released by neurons in the hypothalamus inhibits the production and release of certain hormones from the pars intermedia or 'intermediate lobe' of the pituitary gland. In affected horses, these neurons degenerate thus reducing the amount of dopamine released. As a result, cells in the pars intermedia become hyperactive (and often enlarged) and produce large amounts of a variety of hormones including ACTH (adrenocorticotropin hormone). However, it is not fully understood how the increase in these hormones results in the clinical signs of Cushing's.
- Who is at risk?
Cushing's syndrome is one of the most commonly diagnosed endocrine disorders in horses. It is most frequently diagnosed in older horses but it can occur in younger horses too. Ponies seem to be more frequently affected than horses, but there doesn't seem to be a breed or sex bias.
- 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 appetite
- 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 Cushing's syndrome, with careful management, appropriate nutrition and veterinary treatment, many horses and ponies continue to have comfortable and active lives for several years. Nutritional management of Cushingoid horses and ponies 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, sugar and fructan, the storage form of sugar in grass.
- Feeding & Management Tips
- Choose fibre based feeds that are low in starch and sugar.
- Balancers are the ideal way to ensure that good doers receive suitable levels of vitamins, minerals and quality protein without feeding excess calories, starch and sugar.
- Avoid cereals and mixes - high starch diets may encourage rapid weight gain & increase the risk of insulin dysregulation.
- Consider choosing feeds approved by The Laminitis Trust but remember that these are not the only suitable options.
- If weight gain is required oil can be added at up to 100mls per 100kg of bodyweight per day to provide additional energy (calories). However simply adding oil on top of your horse's current feed may the unbalance diet, so consider choosing a feed that already contains a higher level of oil - speak to nutritionist for more advice.
- Feed small meals - a maximum of 2kg for horses, less for ponies.
- Do not restrict forage intake to less than 15g per kilogram of bodyweight per day dry matter. In practise this equates to approximately 18g of hay per kilogram of bodyweight per day in horses and ponies without access to grazing - speak to a nutritionist for more advice.
- Have your forage analysed for water soluble carbohydrate (WSC-sugar plus fructans) which should ideally be less than 10%.
- Soaking hay for 12-16 hours in tepid water can reduce WSC by up to 50% but results are variable and in hot weather soaking for more than 6 hours is not.
- Make all changes to the diet slowly, this includes changes in forage and grazing.
- Maintain a regular exercise programme where possible.
- Additional antioxidants such as vitamin C may be beneficial although not scientifically proven.
- Grass can continue to grow for most of the year, however it grows more rapidly in spring and autumn therefore extra care should be taken during these periods
- Consider turning out late at night until early morning when fructan levels are likely to be at their lowest - remove from pasture by mid-morning at the latest
- Avoid pastures that have not been properly managed by regular grazing or cutting. Mature stemmy pastures and those stressed by drought or overgrazing may actually contain high levels of fructans
- Restrict grass intake by using a grazing muzzle (that still allows for drinking), grazing with sheep, turning out in a sparse paddock or by strip grazing (remember to back fence and not give access to too much grass in one go)
- Turning out for short periods unmuzzled may encourage 'gorging' and may therefore be counterproductive - in a recent study ponies were seen to consume almost 1% of their bodyweight in only 3 hours
- Make use of ménages and wood chipped areas for turnout time without access to grass
- Do not turn horses out onto pasture that has been exposed to low temperatures in conjunction with bright sunlight i.e. sunny frosty mornings
- Do not allow grazing on recently cut stubble such as after hay harvest
- In known laminitics, consider no grazing whilst providing suitable forage