I had a pair of mice, and one died after 18 months. I believe it was lack of Vitamin A. I think she went blind and could get to her food. The other lived another 6 months. Strange how both ate same diet, but one was ok. The first one to die, was sick for a long time. Smaller, and a cancer on her ear. Shaky when moving. I had 2 dogs. One died after 11 years, other is still fine. I think the dead one had cancer. Just bad luck. A bit less fur, and the sun get more exposure, or something.