I show chickens, and after doing some research, have decided to vaccinate all of my chicks for Mareks, Newcastle/Bronchitis and LT....as these seem to be the big scary ones. Well, after reading the N/B package insert- it said that this vaccine should not be given to chickens over 16 weeks old. I vaccinated everything anyway, and now I have 2 older pullets that had previously been laying eggs for about 2 months, quit laying. Has anyone else had this experience? It only affected these 2 birds, which unfortunately, were 2 of my best pullets. Do you think they will ever resume laying again? The vaccine did not affect my older hens at all.