Life expectancy, its relation to sexual activity and body weight in male inbred mice.

Body weight of male mice of five inbred strains caged in groups of five was determined three times between the ages of 80 and 100 days, representing the individual fully grown body weight. Sexual activity of each mouse (number of ejaculations and intromissions) was estimated under competitive conditions between the ages of 120 and 150 days in eleven repetitions. Within all inbred strains only about half of the males displayed sexual activity when confronted with an estric female. The other do not. The animals remained in their cage groups until natural death after 727 +/- 215 days (C57BL/6), 638 +/- 260 days (BALB/c), 630 +/- 187 days (CBA), 560 +/- 230 days (DBA/2) and 317 +/- 62 (AKR) days. Only amongst the sexually active animals did individual life span correlate with the number of ejaculations. This was seen in C57BL/6, CBA and DBA/2. Particularly sexually successful animals, carrying out the most ejaculations, live 10-20% longer than their (subdominant) competitors displaying less sexual success. Sexually inactive males (characterised by no ejaculations and less other sexual activities) show that this characteristic of their personalities imposes no limitation upon their life expectancy. Fully grown body weight and the individual life span correlates within the strains DBA/2, C57BL/6 and BALB/c. Medium-sized animals have a greater life expectancy than small or large ones.