Belly rot is caused by an overexposure to moisture. 50-60 percent humidity at all times is a must. In shed I keep the humidity at 70-75%. I don't think the 65% humidity would have caused it but I'm not a vet so I can't tell you for sure. Also unless you are breeding the temps should be a constant 92-94 hot side and 82-84 cool side all year round. Your vet will know what they are doing as far as treating the ailment. Good luck and I hope he gets better for you!