Abstract
Some of our breeding programs include the use of Prm1 male Homozygous mice which are naturally sterile. This removes the need to use vasectomized males to induce pseudopregnancy in female mice. These males can be kept for up to 9 months and are housed with a companion female. During the timed mating period the companion female is replaced with a new female. This procedure can occur at regular intervals causing a significant increase in cage activity; one of our objectives was to determine whether this was as a result of timed mating. We wanted to investigate the disruption caused to mice during the day of the swap and how long it would take for the cage activity to return to pre-replacement baseline levels. We hypothesized that this impact would be reflected as a significant increase in cage activity, which in itself may not be a result of a negative experience but the potential of repeated disruption to their activity pattern should be considered. We used a well-known home-cage monitoring system to assess changes to the activity pattern in cages when a companion female is replaced. Data from our initial study showed that in the 2-h period after the female is replaced there is a significant increase in cage activity compared to the same time frame on the previous day. In the subsequent study, where no cage change occurred, an increase in activity was also observed when females were replaced; this returned to baseline after approximately 4 h. Prolonged activity during the rest period of mice (over 2 h) could lead to them being fatigued during their active period; therefore, as a refinement we propose that timed matings be performed later in the day, at a time when the animals are active.
Highlights
The use of sterile male mice to induce pseudopregnancy in female mice assigned for the implantation of embryos is a vital component in the production of Genetically Altered Animals (GAA)
There was no significant difference in activity of female replacement or cage activity for the timeframes
We observe that the cage activity at the typically quiet time 10:00– 12:00 h is very similar in all the days leading up to intervention Day 6 and, we notice a significant increase for Grp_1.m on Day 6 as compared to previous days and Grp_2.m (Figure 6A)
Summary
The use of sterile male mice to induce pseudopregnancy in female mice assigned for the implantation of embryos is a vital component in the production of Genetically Altered Animals (GAA). One refinement to GAA production has been the development of genetically sterile mice, in particular the double transgenic Protomine (Prm1) strain of mouse. The male mice born with the dominant Prm1-EGFP transgene were found to be naturally sterile and can be used as a replacement for vasectomized mice (Haueter et al, 2010). These GAA mice have successfully replaced the need to use vasectomized male mice for generations of pseudo pregnant females in our facility. As the male mice utilized to induce pseudopregnancy cannot subsequently be re-housed with other males due to fighting, these mice are individually housed for up to 9 months depending on their breeding
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