What is Cushing's Disease in Horses?

SARAH: "What is Cushing's, and what is it caused by? What can I do to manage it?"

DR LYDIA GRAY: So you'll help me make sure you answer each of those questions. So the first one is--

SARAH: I can keep track of the questions. I will not be doing the answering.

DR LYDIA GRAY: What is Cushing's? So the other name for it, the name that your veterinarian might use is pituitary pars intermedia dysfunction, or PPID. So here we go with the acronyms. And it's a collection of clinical signs that are associated with an endocrine dysfunction.

So what happens is your pituitary gland-- and there's three parts. That's why it's narrowed down to the middle part, pars intermedia-- is under negative inhibition, so it's being kept in check by another section of the brain called the hypothalamus. And the hypothalamus, one of its many jobs is to send over a signal, a neurotransmitter, dopamine specifically, to the pituitary and say, "Calm down. Keep calm and carry on. Just chill." And then, everything's fine.

But as age, oxidative stress, happens to horses-- so this is a senior horse disease-- then, the hypothalamus doesn't do as good a job sending over that signal and the pituitary is unchecked and it becomes enlarged and overactive, dysfunction. And so then, it releases some hormones. ACTH is probably the best known of those. And then, we have this collection of clinical signs.

And so it might be a long and curly hair coat, which we call hypertrichosis. It could be weight loss, specifically muscle loss. And here, I'm thinking over the top line and the bottom line, or the underline, the belly. Increased susceptibility to infections, so the immune system is dampened. Laminitis is a problem. They might urinate more frequently and then drink more.

So it is truly a cluster or collection of clinical signs. And together, you begin to notice things not quite right with your horse, even behavior, attitude changes. And you talk to your veterinarian. And then, they come out and test.

SARAH: So we've got what is it, what is it caused by. What can I do to manage it?

DR LYDIA GRAY: So well, I guess we can go on with your vet. So your veterinarian comes out and diagnoses it. And this is a pretty simple test now. Now, it's just an ACTH test. And it's a one time blood draw. So it's pretty simple. It used to be an overnight and fast and you give something and that's all done.

So once your veterinarian has a number, there is an FDA-approved medication for it called Prascend, which the active ingredient is pergolide. And so you give that and you retest. And you look for the clinical signs, the long curly hair coat. These horses, they don't shed out in the spring. That's sort of the classic, what you see.

SARAH: So if these aren't working, might have a problem.

DR LYDIA GRAY: Call your vet. That's right.

So if the blood work comes back, like in 30 days, better and the horse begins to shed out, then you're on the right track. And if not, then, maybe test the blood again. And maybe the medication needs changed. So that's the medication side of it.

There are some supplements, specifically targeting the muscle loss. So you can add back in extra amino acids, lysine, methionine, and threonine to help build up that top line. You can add in some antioxidants, because we know the hypothalamus is not working properly, because of oxidant-induced injury. So get those going.

Some omega-3 fatty acids to help balance the inflammatory and anti-inflammatory side. And there are some other herbs. Adaptogens would be great to support the immune system.

Feeding, you don't know what you'll need to feed or how you'll need to feed, unless your veterinarian does the test for Cushing's, as well as a second test, the test for insulin resistance, because you can have Cushing's alone. And that's pretty manageable. You just feed to the body condition score that the horse should be at. And you feed to their teeth and whatever issues they might have.

But if they also have insulin resistance diagnosed with the oral sugar test, then you need to reduce the sugars and starches. So it's things like soaking the hay or having them wear a muzzle or not feeding early or at least reducing grain and watching the treats that you give. So no longer a bag of peppermints or a bag of carrots. I know people that do that. But you don't have to do those things, unless your horse has insulin resistance as well as the PPID.

SARAH: You talked a couple of times about a word that I think we're pretty familiar with here at SmartPak, or a phrase. But I think some of our fans might be less familiar with. And it brings me almost back to the same grade that I was in when I was learning about photosynthesis, oxidation or oxidative stress.

And so the way that I think most people might be familiar with it is, if you think of oxidizing, you might think of rust on metal. And so, hopefully, unless we're talking about the horse shoes, a horse shouldn't be experiencing rust. So what kind of oxidative stress are horses exposed to? And how does that happen?

DR LYDIA GRAY: So think of normal things like sunlight, with the ozone layer and all of that and chemicals and just the environment and life itself. I mean, exercise induces injury oxidative stress. And so it's when free radicals are generated and you need antioxidants in your body to capture them as they are generated. So Vitamin E is an excellent antioxidant. Vitamin C, Vitamin A, there's some other ones.

I like alpha lipoic acid, because it's both fat and water soluble. So it can go everywhere and gather up these harmful agents that are released. So if you have antioxidants on board through the diet-- selenium is one. It partners with Vitamin E-- then, you're in better shape than if your horse is dealing with this oxidative stress on his own.

SARAH: That all horses are exposed to all the time.

DR LYDIA GRAY: All the time. Yeah. So if there's more oxidative stress going on, then they're going to burn through their normal amount of antioxidants they have. And so it helps to have more.