Sickest cow I have ever seen came right after she calved. The calf was a true breech, so the vet came and after a hard pull got it out. Calf was good, cow was good, but after about the month the cow wasnt putting on any weight. After two months she was skin and bones, and was starting to smell. Vet came out, said she'd ruptured her uterus through to her bowel. All the manure and urine was pooling up into her uterus and festering. We took the calf off her and she lived for about three more months, with numerous shots. She eventually went into kidney failure, she went blind and her skin turned to hard leather. She was shot in the end.
Similarly, the other one that comes to mind is my doe that was euthanased last month. She also ruptured the uterus and bowel because she got a kid stuck in the pelvis. However, she only lasted a day. I've never seen an animal get so crook so quickly. It was sickening really. I still beat myself up about it. Poor girl.