Restricted mating windows and thrombospondin 2 gene deletion improve the precision of parturition timing in mice†

Mice are an important model organism for studying reproduction, parturition timing, and embryonic development. Previous reports indicate that limiting mouse breeding periods can reduce variability in fetal weight. To expand on these findings, this study sought to determine whether a restricted breeding window affects mating receptivity, precision of parturition timing, and pregnancy outcomes compared to standard overnight breeding of two common wild-type strains (C57BL/6J and CD-1) of laboratory mice. Since thrombospondin 2 (Thbs2) knockout (KO) mice exhibit premature cervical remodeling without a shortened gestational length, we examined whether these mutant mice experience more precise parturition timing compared to their wild-type (WT) controls. Our findings revealed that the percentage of CD-1, but not C57BL/6J, female mice that were copulatory plug positive was significantly (P < 0.0001) reduced following a 2-h restricted mating period in the morning or evening compared to overnight breeding. Conversely, using a 2-h restricted breeding period in the morning or evening significantly (P < 0.0001) reduced the pregnancy rate of C57BL/6J, but not CD-1, female mice. Additionally, the variance in the gestational length and the timing of parturition was significantly (P < 0.0001) less in C57BL/6J and CD-1 females bred during a 2-h period in the morning compared to either strain bred overnight. Interestingly, Thbs2 KO mice mated overnight had the shortest variance in parturition times. Pregnancy outcomes were not significantly impacted by breeding schedules or Thbs2 genotype. Collectively, these data reveal that restricted mating windows and deletion of the Thbs2 gene lead to more precise timing of parturition.