For the most part, I've been really lucky with my horses. There have been some scrapes and cuts and a couple of infections that I treated myself. This year is the first year I've had to deal with thrush and only in one horse.
In the last 20 years or so, we've only lost one horse that didn't just die/be put down from old age. He got some rare inflammation in his intestines and, in spite of the vet doing all he could for several days, lost the fight. They're still not sure what caused it.
ETA: Oh, wait, there was one mule that was one of the first victims of West Nile before anyone really knew what it was.
Other than that, it's just been pretty typical working horse stuff. A stone bruise or pulled muscle here and there, a very occasional abscess. My brother had a horse bow a tendon pretty bad but after some turnout, he was fine, as sound as ever.
I'm exceptionally grateful that I've been taught all I have. For the most part, I can completely avoid going to the vet unless it's really serious or if I need bloodwork pulled for coggins or whatever. Most minor to moderate injuries/infections, I can treat them myself just as effectively as the vet....without the $100+ bill to go with it LOL.