>>35245075Rats do not have a breeding season, although very hot or cold temperatures will reduce breeding. Females of breeding age come into heat all year-round, every 4 to 5 days, unless they are pregnant. Even then, they may come in heat once or twice early in the pregnancy. Each female usually has a regular schedule that can be marked on the calendar, but it can vary. Each heat usually begins in the evening and lasts most of the night.
