The Placental Scar as a Measure of Fertility in Rats

Abstract

Studies of reproduction and population dynamics of wild mammals have been handicapped by the absence of a technique for determining reproductive histories of individual females. For captive animals it is a simple matter to count the number of young produced by a given female, but the unmeasured effects of confinement make it impossible to apply these figures to animals living in the wild state. Various workers have suggested that counts of the pigment spots left on the uterus at the of implantation might serve as indicators of reproductive history. These spots, commonly referred to as scars,1 uterine or sites have been noted and are located on the mesometrial side of the uterus at the base of the mesentery. Deno (1937, 1941) described the details of the formation and involution of these structures in the laboratory mouse and Masson and Selye (1942) described the movement of the placental scar to the mesometrial site in the albino rat. No critical work has been done, however, to test the reliability of placental scar counts as indicators of the number of young produced. In some species the presence of placental scars has been noted and a few counts have been made. Sooter (1946) found in muskrats from 0-26 scars with an average of 14.1 scars per female. Stuewer (1943) concluded that a female raccoon had had 4 young because the uteri had 4 scars. The object of this investigation was to compare the number of young produced by each female rat with the number of placental scars found in each reproductive tract at autopsy.