What is this?

[Elliott760]

Can anyone tell me what this is? I have 9 hens and 1 rooster (4 cornish 5 buff orphington-hens)(blue cochin rooster) the cornish shown is the only one with these signs, and out of the buffs 3 of them have this feather loss. All chickens are around 10mo old and did not molt in the winter(I live in S TX wasn't really a winter) All the birds have been wormed and they get dusted often. These are my first chickens so I am unsure as to what exactly this is. They are also all still laying eggs I get about 6-8 a day and are eating fine with lots of energy.

 

[Ducks4us]

If its only in that area i would think its from the rooster mating.

 

[aart]

What are you 'dusting' with?
What and how exactly are you feeding?