Delay of Implantation in Super-ovulated Mice subjected to Crowded Conditions

Abstract

IT has long been established that delay of implantation may occur in lactating mice. Recently, it has been noticed that delayed implantation may also occur in super-ovulated females kept in conditions of mild crowding. Twenty-two female mice (TT strain) were placed, when aged about 30 days, in a cage measuring 24 in. × 14 in. × 7 in., which had one drinking and one eating station. They remained in this cage for the duration of the experiment. When the mice were 59 days old and weighed 30–35 g, the super-ovulation procedure was commenced. This consisted of injecting, intraperitoneally, 3 I.U. pregnant mare serum (‘Gestyl’, Organon) and 3 I.U. human chorionic gonadotrophin (‘Pregnyl’, Organon), the former 43 h, and the latter immediately, before mating at noon on day 0, when 7 males were put into the cage containing the 22 females. The males were removed at 9 a.m. on the first day and the number of females having mated, as evidenced by the presence of vaginal plugs or spermatozoa in the vaginal smear, was noted.