Ovarian Structure in Mice Lines Selected for Weight

Selection for body weight at 49 day of age (s and h, downward selected lines; s' and h', upward selected lines) affected reproductive traits in CF1 mice lines. The objective of this study was to compare ovarian structures in females of these lines, as well as in unselected controls (Line t). The number of ovarian follicles (N), follicle diameter (FD), number of corpora lutea (CL), litter size (LS), and body weight (W), were recorded. There were significant differences among lines for N, FD, CL, LS and W; means values for the lines with the greatest difference for post-pubertal females were: N-s = 19.3 and N-s' = 32.7; FDh' = 161.7 and FDs' = 178.2; CLh = 10.3 and CLs' = 21.9; LSs = 6.0 and LSh' = 11.1; W-h = 18.9 and W-s' = 32.4. There were also differences between positive lines; Line s' had a higher proportion of large follicles in pre-pubertal females, a greater capacity to convert these follicles into CL, but a lower capacity to maintain embryos until term than Line h'. For negative lines, Line h apparently had a reduced incidence of embryonic loss when compared with Line s. In conclusion, selection for body weight modified ovarian structure, as well as reproductive efficiency.