Baby chicken with feather of Quill mite?

[antoniawarren]

ok. I am new. My first time having chickens. 2 chicks, one starting to look different so I started to investigate and I got Livermectin 5mg Pour-on from Ivermax. I am so desperate I put 1/2 ml on the clear neck and treat also the brother because he started to look like he is getting the same. Do you think I did it right? they both are always together. What is the next step? how do they get this? what can I do to prevent this?
Thanks!!!!

 

[antoniawarren]

Also, do you know what type of chicken are these? do one of the chicks looks like a rooster because of the tail?