We have a horse who has Cushings, my buddy Solo.
Usually, a curly coat when he hasn't had one before is a symptom, along with problems shedding it out. A pronounced hump in his withers, and craving salt are others. Solo used to eat a normal salt block in a day. Weight loss is another, unless he has a history of being a hard keeper.
Cushing's is a tumor, so there really aren't many ways to prevent it. It's very manageable, Solo has had it for years and years and does fine.
That's all I know from being around Solo. Good luck with the little guy, he is a cutie.
"Sit tall in the saddle, hold your head up high. Keep your eyes fixed where the trail meets the sky. And live like you ain't afraid to die...don't be scared, jut enjoy the ride." - Chris LeDoux