Your vet is right, that you really couldn't have done anything differently. You brought your bun in right away at the start, so after that your information about what's going on and what to do is coming from the vet. The blood work didn't show evidence of the infection. If the infection was in the digestive tract, without the diarrhea being present at the start, I wouldn't have thought to treat for bacterial enteritis just based on my rabbit having symptoms of stasis, and I wouldn't have thought my vet would pick up on this either.
You know the saying about hindsight. But at the start, by all appearances you were dealing with a simple case of stasis, and an antibiotic isn't typically given unless there's some indication of infection being the cause, which indication you didn't have. Even if the vet had given you an antibiotic, the usual one given is baytril and it's likely it wouldn't have been that helpful in treating this type of infection. Without having seen the diarrhea earlier, it would have been difficult to know there was a bacterial infection present. If it was the clostridium bacteria, it's such a toxic bacteria that it does cause death very quickly and isn't easily treated because of this.
I know how hard it is to look back and wish you had done something differently, but I think it's always this way when we lose a pet. You just have to keep reminding yourself you did all you could, and that your bun had a happy life with you.
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