Help with illness symptoms

[MikeWu]

I have 8 red pullets and a few weeks ago their rooster died in an accident. I went to a slaughter house and bought them a new rooster, which in the first few days didn't look very energetic, dozing off often during the day. He's more energetic now, but he might have brought some diseases to my hens as they stop laying eggs all together. I found a few hens dozing off, and today one hen didn't run after food as others when I tossed to them. This hen's foot skin appear to be darker (brownish) than usual. I locked her in a cage to quarantine her, and left water with tetracycline in it (advised by a sales lady at our feed store).

What could be the disease with these symptoms? How do I treat them besides giving them tetracycline?

Thanks for the help!

 

[ramirezframing]

check for mites, with a heavy load of mites birds lose weight and sit alot and can even die other than that I am not sure

 

[MikeWu]

Thanks for the help! I checked the chickens under their feathers, and saw no bugs at all (I assume I can see mites with naked eyes, right?).

And I just saw another chicken with similar symptom: inactive, not running after food, etc.

Any advise on this issue is greatly appreciated!

Mike