Is there any discharge? Have you smelled it?
Possible things:
Egg Bound
Prolapse - doesn't look like prolapse to me though.
Vent Gleet or yeast infection
Rotraviral Enteritis causes swelling of the vent
Possible things:
Egg Bound
Prolapse - doesn't look like prolapse to me though.
Vent Gleet or yeast infection
Rotraviral Enteritis causes swelling of the vent