An untreated abscess can become infected causing serious complications. If you can see the abscess - dig it out as best you can to allow drainage. Laminitis - is caused by some sort of stress to the system which in turn causes inflammation in the hoof, resulting in the capillaries bursting and dying and the sensitive white line loosing its attachments to the coffin bone. Having a fingernail being torn loose is very similar to what is happening. Most Laminitis is in the front feet, but it can be in just the hind feet, one foot, or all four.
Founder is when the support is gone and coffin bone falls.
Abscesses usually occur in the beginning stages of Laminitis - in fact we have actually had pus dripping out the bottom of the hoof on really bad cases. The best way to deal with Laminitis is to prevent it from happening in the first place. Keep your feed grains, dog food, and cat food, out of the reach of donkeys. Be very careful of feeding cattle feeds. Make sure your hay is not moldy.