This is an open bug that was archived. I am not sure if a new bug report is meant to be made.
Animal aging is turned off in options. Aging is turned off for all sims.
I have a save file I have p...
Ideas
I only noticed this when I used a sim from a different household to visit the one with farm animals. It had been a few days since I had last played the one with the chickens and had left one of them as a chick upon last save. But as soon as my new sims visited that lot BOOM, they all died including the chick.