I just moved one my horse about 2 weeks ago. I always worm after a move, no matter when I wormed last. Your horse wont be harmed by worming him again, if that is what you are thinking. There are plenty of barns that worm horses on the 1st of every month with no harm done (except for building resistance), but one time wont do that with your horse. If you really want to know his worm count, pull a fecal and send it to your vet. That's what I do with my guys every 3 months and if the count is high enough, I worm them.