when to worm

[catdance62]

We have a flock of chickens that is about 13 weeks old. When or should we worm them? They free-range during the day but come in to their enclosure & coop at night. I keep dairy goats and I know when then need wormed, but this is our first year with chickens. They seem healthy and I do not want to over-worm and build a resistance as can happen with goats.
Thanks in advance!

 

[Chickaroo!]

I'm not positive about when to worm, but I know I've seen alot of threads on here that says alot of people don't worm until they acutally see a worm in the poo. Some have never wormed. Maybe someone smarter then me will have a better answer for you!