More and more of our horses and ponies seem to be being diagnosed with the condition that used to be called Cushing’s syndrome, but is now termed PPID or pituitary pars intermedia dysfunction. This condition is classed as an endocrine disease, or endocrinopathy.
The disease is caused by a degeneration of dopamine-producing nerves in the brain, causing much less dopamine to be produced, which then has an impact on a variety of other hormones, allowing their levels to raise to abnormal levels. Why some horses are affected with this disease is not understood, but it does seem to be becoming more common. It may be due to oxidative stress, and some researchers propose this may occur due to altered glucose metabolism.
Symptoms of the disease caused by the hormone imbalances include a long hair coat that is not shed in the spring, excess drinking and urination, loss of muscle and a pot-bellied appearance, lethargy, fat filling the dips above the eyes, inhibited immune function, insulin resistance and laminitis (which may occur in the autumn or winter). Not all affected horses have all the signs, and in the early stages of the disease, no symptoms may be present.
Equine PPID is challenging to diagnose in its early stages, but more tests are becoming available and your vet can advise if you suspect your horse may be affected. Long-term drug treatment (usually with pergolide, a dopamine agonist) is necessary to reverse the symptoms and reduce the risk of laminitis and chronic infections.
Horses with PPID need very careful management and feeding to ensure they stay healthy. They should be fed a good quality diet with adequate good quality protein especially if they are showing many of the symptoms. They also need a diet with a low glycaemic index, so low water soluble carbohydrates (WSC) and restricted grass intake. They must be fed a good multi-vitamin and mineral mixture either in a supplement, balancer or low-starch compound feed. Overweight PPID horses need to go on a slow weight-loss regime until they reach a healthy weight, but other affected horses may be over-thin and need a higher energy, higher protein diet to help them gain some weight and condition.
Antioxidant and immune-supporting supplements are recommended, as is the herb chasteberry or Vitex agnus-castus. Although research is yet to confirm that chasteberry makes a difference to PPID-affected horses, it contains constituents that bind at dopamine receptors so it may well have a beneficial effect.
With good veterinary attention, daily care and feeding, PPID-affected horses can go on to live healthy lives for many years.