I find the whole momma hen thing confusing also when it comes to Marek's. I thought, from what I read, that you are not supposed to have the babies around the adult chickens until they are past the five-month mark. So I guess having the broody hen and raising the chicks in the barn with the flock is out of the question. We started our flock with 25 RIRs that we bought from the hatchery and had vaccinated. Then I bought an adult silkie hen and seven chicks and I feel pretty certain they were not vaccinated and I didn't know enough at the time to inquire, but I would bet one of my last dollars they are not. I bought three more adult silkies last November and, again, didn't know anything about vaccinating for Marek's so didn't ask, but don't think they are vaccinated. Now I have my two hatches and others that are coming as we speak. From what I read, it didn't seem like it would do much good for me, except to vaccinate the ones in the incubator. Four of the eight chicks have been out and about in the yard on pretty days with momma. I let both mommas keep their babies so the second set of babies are cuddled up with an adult. I didn't see, from the research I started on late last night, that it would do much good to vaccinate adults or older chicks. I told my husband this morning what I had found it (it was him who originally asked about the Marek's vaccine) and said I just don't think I want to hatch any more babies. We (him) had to put down a chicken at the end of last year and it was very difficult to know we had to kill something, even though it was for the best. So I do agree on vaccinating. Even if you keep a closed flock, it seems like there is so much that can be contracted from down the road in the wind or wild birds flying over the yard.