Equine Metabolic Syndrome is defined as a “Clinical syndrome associated with an increased risk of laminitis that includes insulin dysregulation and any combination of increased generalised or regional adiposity, weight loss resistance, and altered adipokine concentrations.” https://sites.tufts.edu/edu/equineendogroup. Donkeys are prone to Equine Metabolic Syndrome due to their physiological adaptations to survive in resource poor environments. The donkey has a lower nutritional requirement than a pony of the same size, but is often exposed to excess feed with high non- structural carbohydrate levels. In addition, they are generally given little exercise.
Donkeys and many small pony breeds are considered to be relatively insulin resistant- which has a survival advantage, but also leads to, and is linked with both hyperinsulinemia and obesity.
As well as clinical symptoms we need to test for insulin dysregulation. Resting insulin levels have very low sensitivity /high specificity and should not be relied upon as a sole test. At The Donkey Sanctuary we use an oral carbohydrate challenge using Karol Light (corn syrup). As donkeys are at increased risk of hyperlipaemia we do not starve patients before testing, but have a standard protocol that involves the donkey only having access to straw for at least 6 hours prior to testing. We then give 45ml/100kg of syrup and obtain baseline blood samples. A second sample is taken 60-90 minutes later to measure serum insulin, which should be below 60mU/L.
At present adipokine testing is not validated for donkeys.
There will be cases of EMS that do not demonstrate obesity and cases that also suffer from concurrent PPID, so in some cases further diagnostics will be warranted. In many cases management of EMS relies on improving the dietary management of the donkey, and initiating a controlled weight loss programme. Ideally, the exercise is increased, but this will be dictated by whether there is any underlying lameness. To prevent boredom in cases of dietary restriction there are several ways to modify and enrich the stable environment.
Medical treatments exist: metformin can be used to reduce glucose absorption enterically and help in transitioning a donkey to pasture; a thyroxine derivative may be useful to increase the metabolic rate.
Pituitary Pars Intermedia Dysfunction (PPID) is seen in donkeys and, as many are kept until they are geriatric it is seen relatively frequently. The condition is known to be associated with an increased risk of immunosuppression and laminitis. Affected cases may have obvious clinical signs such as hirsutism, muscle wastage and polydipsia. However we rely upon testing suspect donkeys for elevations in ACTH to detect cases before such signs are reached.
PPID results in hyperinsulinemia, which is a risk factor for laminitis. We also find these cases may have higher faecal egg counts, higher ectoparasites burdens and delayed wound healing.
Treatment of the underlying disorder relied upon the use of pergolide- Prascend at 2µg/kg. As the drug can suppress appetite donkeys need careful monitoring when on the drug and may need to start at lower doses. Testing In autumn when the levels are at their highest is considered the best time to discriminate for positive cases.