Hi Looking for advice , we breed chicks and have had a lot of success. We recently bought some 5 austrolorp chicks n 3 leghorn chicks , we kept them isolated from our chicks , but we lost 5 of the chicks we had just bought within a few days. We kept them quarantined for 2 weeks and they seemed healthy so we put them in with our chicks n now we have lost 3 of ours over about 1 week. The chicks get tired and drowsy then within 24hrs they are gone . My partners grandfather used to be a chicken farmer n has had a look at the dead chicks and inside they are very healthy. Does anyone have any ideas what it could be ? ?