Considering what a pest shitters can be, it's amazing when you think about how fragile they actually are.
I am going to list some things I've known that has caused them illness or to die.
1) Ear mites. Ear mites are a real pain in the ass, and bother your stock a lot. You need to check ears on a regular basis, as these are contagious and will spread through your shitter herd in no time, if you are not careful.
2) Fly strike. I am not posting any image for fly strike because this is too disgusting, and is the big reason why you check your shitter's ass every day. If it gets dirty, which it shoudln't because these are clean little guys, it will attract flies which lay eggs on your shitter's skin. These will hatch into maggots and begin to eat him alive. Don't let it happen. This happens most to old shitters, or ones which have dumb long fur.
3) Being wet. Shitters hate being wet. Don't leave them in a situation where they will get rain on them and can't get dry. Always provide shelter.
4) The cold. Shitters are pretty tough little guys when it comes to cold. But as any asshole knows, leaving them out when it's too cold is asking for trouble.
5) The heat. The flip side? Shitters do not do well in the heat, which can kill them. It makes your breeders temporarily sterile too. I make sure to provide constant water, and if it gets too hot, I put frosen bottles of water in with each shitter. That helps keep them cool, as can a fan system.
6) Coons, snakes, weasels etc
7) Myxomatosis. A real shitty disease that will lead to a long lingering death for your rabbits. Either vaccinate, OR make them into dog food at the first sign of it. There is no cure.
8) The wrong diet. A shitter should mainly eat hay. Like 90% of his diet. Give them green treats as well, by all means, but not a lot. These can upset their stomachs, and lead to diarrhoea and fly strike. They can eat grass, but not lawn clippings. Don't ask me why. I don't know.
9) Being handled wrong. Never hit your shitters. Apart from anything else it doesn't know it's being punished, so what is the point? You need to handle them with care, as they have delicate bones, and can easily do themselves an injury if they struggle. This is why I want you to know it is important to handle your stock on a regular basis.
The thing is, the shitter is one of the cleanest animals you will ever meet, provided that he's been de ballsed. This also matters because it will make him friendlier and stop him fighting or messing around with other rabbits. You gotta do it.