Efectos de la Selección y de la Superovulación en las Pérdidas Gestacionales de Ratonas CF1

the ovarian structure was modified as a consequence of weight selection in a pair of mouse lines selected for high (s') and low weight (s). lines were founded from an unselected population of cf1 strain (t). the follicle diameter and the number of the ovarian follicles and the corpora lutea were higher in s' females, but they did not reach a larger litter size at birth, may be, by an increase in the gestational losses. in these lines, the co-effects of long-term weight selection and ovarian stimulation were tested to evaluate if they increased gestational losses. two groups of females per line were employed: without and with ovarian stimulation (5ui of ecg and 5ui of hcg). females were slaughtered at 56-72hs and at 7 days post-breeding and after first parturition. the number of corpora lutea (cl), embryos (e) and implantation sites (si), and litter size at birth (tc) were observed. total losses (pt) and corpora lutea (pcl), embryo (pe) and fetus (pf) losses were estimated. mean cl, e, si and tc varied in the same direction of the selection made and they were significantly higher (p<0.05) in stimulated females, though not for tc. line s' had a higher reproductive potential but a greater biological cost (higher and later gestational mortality) when compared with the other lines. ovarian stimulation produced lower total reproductive efficiencies for the three lines and higher and later gestational losses, mainly for implantation sites. females from unselected line (t), without ovarian stimulation, with intermediate weights, bore larger litters, starting from an intermediate number of cl, e and si, with a lower and earlier embryo mortality, showing to be the most efficient from a reproductive and productive point of view.