I think you can start the pergolide at any time. It is very expensive and usually used when the animals start to get really sick. Other symptoms are excessive thirst and urination, a pot-bellied appearance and of course, the long, curly coat even in summer. George's coat isn't that curly but it is wavy. I'm thinking that they can have bad breath, too, and George does. His breath could nauseate a grizzly bear.
That is nice that you were with your friends horse when he was put down. I've done that myself for a friend. It is kinda gross when they move them and I don't usually watch that part.
My friend's was very curly... and impossible to brush through, it was so curled and course.