http://www.heavensentranch.com/poultryhealth.htm
There is an article on this link that was written by Peter Brown "the chicken doctor" from First State Vet Supply.
It is an interesting article and where I read that vaccinating an older bird may stop the tumor growth. I will say that one chicken that I vaccinated NEVER laid another egg. She was a young bird, and laying every day. I gave her the vaccine and her laying stopped, immediately. Figure that out, but that is the only problem I have seen from the vaccine. When I buy from a hatchery I always have them vaccinated, just for a little security.
There is an article on this link that was written by Peter Brown "the chicken doctor" from First State Vet Supply.
It is an interesting article and where I read that vaccinating an older bird may stop the tumor growth. I will say that one chicken that I vaccinated NEVER laid another egg. She was a young bird, and laying every day. I gave her the vaccine and her laying stopped, immediately. Figure that out, but that is the only problem I have seen from the vaccine. When I buy from a hatchery I always have them vaccinated, just for a little security.