At what age can a new chick be combined with rest of the flock?

you may want to wait until it is about a month and a half or two months old

 

I like to put chicks with a broody momma in with the flock as soon as possible. I actually let my broodies hatch babies in the coop and raise them with the flock from day one. I'd put your momma and baby back in with the others today. At 3 weeks, momma still has protective instincts toward the chick and will let the other flock members know not to mess with it. If you wait, you run the risk of momma "weaning" the baby and not standing up for it.

 

When you do it, observe them for a while to make sure everything goes well, don't just throw them in the tank and leave for the day. Even though the mom hen will protect her chicks if the other hens approach, the chicks will always approach the other hens and recieve a swift peck for their efforts.

 

I think it's a whole different thing if the chick is on it's own, versus with a brooding mom. I was taught if they are on their own to wait until fully feathered (10 weeks, give or take). If they have a "guardian", I think you are fine whenever you choose because "mom" will protect them. It sounds like yours has a mom, so as long as you think mom can handle it you are good to go.

 

This is very true. I have momma hens hatch chicks in the flock from day one and no problems. I tried a few times putting 2month old pullets in with my layers and got dead chicks for my trouble each time. I now keep brooded chicks separate until 4 months or so. It's just so much easier to have a broody hen do all the work, and they love it!