Ten 2-week old chicks just arrived in the mail. One was D.O.A. One died within hours. It soon became clear they were all struggling. They are gasping and mouth-breathing, staying under the heat and sleeping a lot. I contacted the breeder and sent video. He called me immediately, was very nice and told me he had showed the video to his vet, who suggested that the problem was a change in humidity. (It IS sopping wet and constantly raining here.) I started them on tetracycline yesterday, and another one died. If any of these chicks survive, will they all be carriers of some virus that can infect all my other chickens? Should I just cull them all? Is there anything more I should be doing? I ordered six chicks and got 10 because the breeder sent extras. I still have six. I am not sure if I need to seek any other recourse?