Introduction of retired breeder F344/DuCrj rats for aging research

Male retired breeder F344/DuCrj rats of 17 months of age were purchased in three lots and maintained for aging studies until 25 months of age. These rats were compared with male virgin rats of the same strain for survival percentage, body weight and food consumption. In the retired breeders, decrease in body weight and low food consumption were noted after delivery, and one or two months were required for these parameters to return to the delivery level. After recovery, the body weight and food consumption as well as survival percentage in the retired breeders were similar to those in virgins. From our results, we consider that it takes one to two months to acclimatize aged rats.