Incidence of spontaneous post-implantation deaths in CFT-Swiss mice: its suitability to assess dominant lethal mutations.

The primary objective of the study was to determine the incidence of spontaneous post-implantation deaths (DI) in our randomly-bred closed colony of CFT-Swiss mice. These data are required mainly to ascertain the suitability of the strain for their use in dominant lethal (DL) mutation assays, a well validated in vivo mammalian germ cell assay. To achieve the first goal, randomly drawn healthy adult males were sequentially mated to adult virgin females (1:2 ratio) for a period of 8 weeks. Male-based analysis of the 3 major variables viz., implantations, live embryos, and dead implants (DI) were carried out. Absence of outliers and low variation in spontaneous DI, as well as the other variables associated with DL assay were observed in all matings. Secondly, the degree of induction of DI were studied following administration (i.p.) of an acute dose of ethyl methane sulphonate (EMS). EMS induced nearly a 5-fold increase in the DI during the first 2 weeks and a 3-fold during the third week suggesting its DL-type effect only in specific post-meiotic stages of spermatogenesis as reported earlier.