Here are some pictures of two hind capsule sloughs/hoof avulsions. This mare was given hormones so they could harvest her eggs. She foundered eventually on all 4 feet, but the hinds had not been trimmed well for a long time. It is believed the amount of pressure they were under caused the capsules to fail.
This should give you a better idea of how the hooves look during the process. This was sort of an unusual case as the mare was foundered in the front as well, and she spent a bit longer down from pain. The first picture was in the very beginning. The two after photos are the first regrowths of the capsules after 8 months, a little disorganized but not awful. This was several years ago and she is old now but doing well.
Photos Copyright ABC Hoof Care and used with permission.