Here is the situation: I took bantam cochin chicks that I incubated, and put them under my 4 broody large cochins to raise 10 days ago. I have lost 10 of the 30 chicks. I noticed some dying overnight, I thought they got cold or squished. I noticed yesterday that the sick ones have somethings in common. They stand by themselves and peep. They don't run after the hens like the rest. Sometimes they make 'peep' beak movements but don't make a sound. I cant tell if they are ruffled/dull cause they have so few feathers... but they seem to have good skin color (though one chick's legs appeared so bright yellow I thought he must be jaundice...it was this yellow--> :| ) Some of the dead chicks had pastey vents, others did not...in fact I have a few with pastey vents since day 1 that seem fine still. They get weaker and lean forward, and eventually fall over. They die within an hour after I notice they are sick. Their poo looks like regular chick poo- its brown mousse looking with no blood evident. Ive seen cocci infections, this aint it. So far the chicks I lost were all bantams. The large hens I have had for years and they havent lost a chick yet...well except for the occasional accident. They arent sick. The bantam parents I got from a hokey fellow, and he did say 'oh this ones got a little cough' when I picked them up. It's actually a little sneeze...he's had it for a month. I havent heard him do it lately, but one of the hens looks pretty pale lately. Some things that are different from last hatches are, I've spread hay infront of the coop that I had in plactic bags over the winter. Also, I wormed all adult chickens with Ivermectin cattle drench 5 weeks ago (it was all that was available, and those bantams had scaley leg mites! eww!) I keep them quarantined but thought it would be ok to hatch eggs. So did I just introduce a horrible disease to my large fowl cochins? What should I do? How can I fix it? oh i should add, they are in a 4x4x4' square coop with 5 adults, fresh pine shavings weekly, they have been eating blue seal chick starter and drink from a 5 gallon waterer I ought to bleach out... I'd like to treat this myself if possible.