I had a vet that took care of our animals tell me that cows fed hay from areas in Oregon got Cancer, after research the problem was Selenium or the lack of it. The Ranchers Darymen supplemented the cow feed and the problem was solved . .Old age and genetics has lots to do with it. Commercial food is as bad for the animals as it is bad for us,Dogs just died back in the day. The got sick one week and would slowly die. Nobody knew what they died from.
Cheap dog food probably doesn't help either. I buy quality stuff for our dogs. My aunt's dog made it to 17-1/2. My mom's cat was 19. But my cat only made it until 9 last year, bad kidneys. Back in the day we wouldn't have known why my cat died (I had him put down before he was suffering too much).