Despite demonstrating obvious abnormalities of clinical appearance, both the dog and the pony (Plates 1 & 2) are suffering from the same condition; Cushing's Syndrome (hyperadrenocorticism). Hyperadrenocorticism produces the opposite changes in hair coat in the two species. In equines this condition is usually secondary to an adenoma, or hyperplasia, of the pars intermedia of the pituitary gland whereas in the dog the syndrome may be primarily of adrenal origin.
In horses there appears to be insufficient DOPamine being released from the hypothalamus. DOPamine inhibits the pars intermedia of the pituitary gland. Therefore when there is less DOPamine there is less inhibition of the pars intermedia which then increases in size.
Equine Cushing's cases always develop laminitis if they live long enough. They may become immunosuppressed and subject to a variety of parasitic or infectious agents such as helminthiasis or pneumonia. Many cases show muscle loss and become polydipsic and polyphagic; they may be diabetic. A supra-orbital swelling, due to the deposition of a fat depot, is commonly seen giving the eyes a protuberant appearance.
To the trained observer, these cases can be diagnosed on clinical appearance and history alone. The clinical signs include;
Failure to shed their coat in Spring, the coat becomes long, thick and matted.
Affected animals tend to sweat more than normal, they lose weight despite an increased appetite.
They may become diabetic, either diabetes mellitus, (sugar diabetes) or diabetes insipidus. They therefore drink excessively, and if stabled you will notice their bedding is quickly soaked.
They show filling above the eyes. This is fat deposition in the supra-orbital fossae. [Normal horses have depressions above the eyes, you can see these depressions moving when a horse chews].
They become depressed and ill-looking, with dull eyes and they lose the shine on their coat.
They all develop laminitis eventually.
Their body shape changes so that they lose muscle mass, developing a dipped back, poorly muscled neck and quarters with a pendulous abdomen. There is a re-distribution of fat depots. The horse looking thin ("ribby") but gaining a rather "blocky" appearance. This is particularly evident if it has been dieted in the mistaken belief that it's laminitis is due to obesity.
Their resistance to infections or worm burdens is reduced.
Taken From Laminitus