The biggest problem is that most people do not understand the need for clean sampling. The risk of cross contamination is much higher in feathers, either through poor collection technique or just natural feather contamination particularly in heavily stocked aviaries.
Take blood, reduce the risk of false results. It isn't that difficult to do.
I have other opinions on this matter but am not prepared to voice them on this forum. All I will say is that track records speak for themselves. Take that any way you like.
