I'm letting my broody hen hatch out a few chicks. If they hatch, do i have to worry about vaccinating them? I bought my hens in 2007 from MPC and I think they were vaccinated, but I don't know what for. Also, with some vaccinations the birds are carriers for life?? How does that work with chicks? The eggs are purchased from someone else - is there any cross contamination through the egg? I'm confused.......help!