I'm not at all sure that periople is OK myself, even if the horse is in wet footing. Especially if the horse isn't in waterlogged footing. Have you been putting oil or something on them, that would make them(& the hair/skin above) look 'soaked'? And the 'chewed' kind of look to it - never heard of rats chewing (!!) but that's a scary thought! I'm with Wares that it looks like there's probably some skin infection going on. Nutrition may also be a prob that's contributing.
As Gotta explained, that's not a healthy foot though(the 'here's a healthy foot' pic didn't show up tho Gotta, there's just a broken pic link above the Arnd Bronkhurst one), and the periople prob may well be just another symptom of that. That 'ledge' kind of look above the hairline is because the capsule has become pushed up high around the bones - or the bones have 'sunk' within the capsule, which ever way you want to think of it. I'd guess that the extensor process(knobby bit, top front) of P3 is well within the capsule. I'd be getting those shoes off and rehabbing those feet. You can use hoof boots when necessary for work, or, while I think they're still best avoided, because any fixed shoe under those walls is going to be a compromise, at least until hooves are healthy, if you simply must use a fixed shoe, something that provides good support under the foot and which doesn't load it too much peripherally will be vital - such as Easyshoes with pour-in pads. Especially if going a fixed shoe, I'd ensure they weren't left more than about 4 weeks between trims - little & often, to ensure there's no overgrowth and you can continue to get improvement with each trim.