You might also want to start them on Baytril. Almost all birds with blackhead will get a secondary E. coli infection, and for that you will need something like Baytril, or maybe eben your Zactran? Talk to your vet.I believe I remember seeing them a couple of years back? I suppose that my deworming may have killed the carriers but not the pathogen. I will give them some metronidazole in the morning.