Have learned this in a very hard way. a little while ago we purchased eggs to hatch, but only 3 boys hatched. But we had fallen in love with them so they stayed, to be sure of healthy birds we bought 6 young hens from the SAME breeder .
They did not all meet until the following week. Unfortunately we then lost 1 girl we thought at the time through stress with moving, and the breeder said she had never lost any.
During the following week another girl started to limp, the breeder thought she had perhaps pulled a muscle, a visit to the vet and the vet gave an anti inflamatory jab, and kept her away from the others. This did not work, she just got worse. We took some video clips and sent them to 2 other breeders and to a vet, the consenus is Mareks.
A week further on, and just over 4 weeks since the girls arrived and this morning one of my beautiful boys could not get out of the coop, his legs cannot hold him, he, like the other one has other symptoms, irregular eye colour and green runny poops, and also has raised feathers.
I have been advised by the Veterinary Laboratories Agency that now Mareks has been on my property, it will ALWAYS be there. When I come to replace the birds I can only have vaccinated birds, so no buying from a small breeder again.
You think you are doing right, but there is always more to learn.
Apparently with Mareks, birds can be lifelong carriers, and you will never know if you bring a bird into your group has it until you begin to have fatalities, unless your birds have been previously vaccinated of course.
The breeder initially offered to refund the cost of the birds, but is now not answering my messages.
Its been a very hard lesson.
Laine