How old before I start worming?

Duncan will be 10 months old on the 31st, and I was wondering when I need to start a worming regiment for him. I buy the year's supply for my horse, where it alternates on an 8 week basis between exodus paste and ivermectin.

I don't know how much Duncan weighs, and I'm not sure how long the pastes last before they expire. I'm ordering some more today, but I want to get some opinions before I buy extra for Duncan.

Anyway, just wanted to make sure he wasn't too young to have wormers-- I've never raised a baby horse before, so I want to make sure I do everything right.

Nope, he's not too young at all, he probably needs it! We just wormed the 6 month old colt at the barn and it's his second time being wormed.

How much of a dose should I give him?