I have a flock of year old SLW 3 roos 14 hens They all hatched together and have been raised together. Currently they all have red vent/above vent around tail thing going on, it seriously looks like they have monkey butts. I have checked for mite and lice I see absolutely nothing but I dusted them anyway with DE. No one is picking at each other I sat and watched them for an hour. What could this be??