Miss feathers on belly

[BentonWoods]

My parents have about 16 birds and when I visited them recently I noticed that many of them don't look entirely healthy. From under their tail to their partly down their belly are missing feathers and some of them are very red. They also look swollen but I may be wrong since I have never seen the underside of a chicken like this before. I'm concerned that it isn't behavior but we do have six hens who are older than the rest and a different breed, although I have never noticed any rift between the two groups. I only have one picture but I will try to upload more. If anyone has any suggestions or can even point my research in a specific direction that would be helpful. I should add that some of the birds are also missing neck and chest feathers.

 

[AustralorpsAU]

Have they been broody recently? Could they be moulting?

 

[BentonWoods]

Like I said these aren't my birds so I don't see them often but I only saw one that was broody. My concern is that the base of some of their feathers are still there but broken and seem to be full of dirt (I don't know if this is normal), and there are not new feathers growing in. It also seems to be isolated to this spot on most of them.

 

[KYTinpusher]

Has it been muddy there a lot lately and do they have a rooster or two with the hens? It could be that the rooster(s) has been very "busy" with the hens and the grit from the mud is wearing away the feathers and irritating the skin. The feathers should re-grow at their next molt.

Something else to check for is mites or lice. You will have to look very closely as they are very tiny. You may not see adults moving around, but look for the clusters of eggs at the base of the feathers, usually around the vent.

 

[18palm]

Can you explain more detail how it looks if my roo has mites? The color of the skin.
Or you can tell me where should I look the subject about mites. Please