Thank you for sharing your experience. I'm terribly sorry for what you went through and what you're going through right now. Know that you have a lot of support, even from us novice homesteaders.
What you say is very true, not only for large livestock, but also animals as small as rabbits. During my research, I did not realize that rabbits could not eat grass cut by a lawn mower. Had I not been informed, I would have happily fed my rabbits lawn clippings and lost them that same night due to the fermenting grass killing them. At the same time, I would have to move them very slowly off their normal pellets and hay to green grass. Super lucky to have read up just before that feeding rabbits mint can help alleviate tiny tummy issues that can come from switching feed.
But we still miss things and it's best to learn from the mistakes, rather than dwell. Now I won't lie, I'm a dweller. While my rabbits are a success, my quail not so much. I've spent hours staring at the spots where my dead quail are buried and get wrapped up in self-depreciating thoughts. We lost two to drowning in their waterer, one to breaking its neck after being flushed out. So, the waterer now has marbles in it to keep them from drowning and the hutch roof has been lowered significantly to deter violent flushing. I'm happy to have learned from these losses but still struggle to move on. Takes time... Like most things.
We have also thought about having rabbits. I did not know that you could not give them grass that has been in a mower! That is crazy! See you are also giving great advice! Thank you so much for sharing that with us.