For the last year of his life, Chuckie had chronic diarrhea.  He seemed perfectly healthy otherwise and he certainly ate normally.   I lost track of how many tests we did and how many medications we put him on to try to clear up what we supposed was a parasite or a bacterial infection.  None of the medications really helped.  Our vet actually mailed a sample of his excrement to a leading pig vet in another city for an opinion.
Finally, he was diagnosed with Irritable Bowel Syndrome, which at first amused us greatly.  It seems like such an absurd thing for a pig to have, after all, and it didn't seem to bother him in the least, the only symptom being the diarrhea.  We were not amused for long, though. 
Adding fiber to the pig's diet is one way to treat Irritable Bowel Syndrome, so on the advice of our vet, we did that.  The diarrhea cleared up, and we were all happy for a couple of days.  In retrospect, I think it was the worst thing we could have done, as I believe it helped cause his death.
Less than a week after we starting adding fiber to Chuckie's diet, he started acting like he was a bit uncomfortable in the abdomen.  We decreased the amount of fiber we were giving him, thinking that would help.  It didn't.  The next day, he looked lethargic as well as uncomfortable, so I stayed home from work and called the vet. 
The vet checked him over and gave him an enema in case he was constipated because of the fiber.  She did a rectal exam too, as she was worried about the possibility of an intestinal stricture, which is a narrowing of part of the intestine.  I'm not sure how or why strictures form, but I believe humans with Irritable Bowel Syndrome sometimes get them, also.  Pig and human digestive tracts are very similar.  The vet didn't detect a stricture in the area she was able to examine, but of course, she was only able to examine the lower colon.  There was really nothing to do at that point but watch him.
After she left, he took a dip in the pig swimming pool, which gave me a little hope.  A bit paranoid about his condition, I checked on him every 15 minutes or so, and after a couple of hours, he abruptly began to look much worse - so much so that I knew something horrid was going on.  His breathing was labored, he was obviously uncomfortable, and he wouldn't get up.
I called the vet back, but Chuckie died minutes before she arrived.  It was quite sudden and it was unlikely she could have done anything to help him, anyway.  She believed he probably had had an intestinal stricture and it had ruptured.  His death wasn't easy to accept, since he was young and to all outward appearances, he'd been the healthiest of our pigs.  Also, we'd lost our kitty Roo to cancer exactly one week before and Arivaca to lymphoma a little over two months before.

Looking back, I'm convinced Chuckie had probably had the stricture for a while, but it wasn't too much of an issue while he had the diarrhea, as things could pass through it.  Once we added the fiber and cleared up the diarrhea, that was no longer the case and the stricture gave way.  No one could have reasonably foreseen that consequence, but I still feel guilty about it and will likely not ever give fiber to another pig.