We've got a calf that has some sort of crud on his hoof -- right rear. We've been treating it with a topical antibacterial ointment but it isn't getting any better. We stopped treatment for a couple days and he got worse, swollen and clearly favoring the foot. He's still eating. Seems to feel okay. Anybody have any ideas what this stuff might be? Fungus? Abscess? He's had it for weeks now.