Life span characteristics in the male Fischer rat.

Survival data are reported for 572 male non-breeding Fischer rats, representing offspring from brother-sister matings, maintained at a constant temperature and humidity, exposed to twelve hours of artificial lighting and to twelve hours of darkness per day, and fed a standard laboratory diet ad libitum. The mean longevity for these male rats was 642 days and the median longevity was 659 days; the longest-lived individual survived to 1192 days. Animals surviving beyond the median life span for this colony were found to lose a greater percentage of body weight during the last few weeks before death than did shorter-lived animals. Offspring born of parents one year of age showed no significant difference in longevity from those of three-month old parents. Moreover, the longer any animal lived, the greater the maximan weight which he obtained.