Ovulation rate and embryo survival during gestation and the effects of ovariectomy on maternal nurturing ability.

Abstract

Correlated responses to selection for increased litter size were studied in mice. The selected line (L+) was compared with an unselected control line (K') in two experiments. The first experiment provided a profile of correlated changes in female reproductive traits at d 0, 6, 14 and 18 of gestation. Experiment two examined the effects of ovariectomy on d 18 of gestation, sham surgery and no surgery on litter size and maternal performance. Females of the L+ line had increased (P less than .001) body weight, ovulation rate and uterine length at d 0 of gestation compared with K' females, but uterine weight and ovarian weight did not differ. Positive correlated responses (P less than .001) in uterine weight and length at d 6 and 14 of gestation were associated with a larger number of viable fetuses. Space per fetus was reduced (P less than .001) in the uterus of L+ females, but a lower fetal mortality was still maintained in L+ throughout gestation. Prenatal survival was about 10% higher (P less than .06) in L+, the major difference (P less than .01) occurring before implantation. A second experiment was conducted to determine the effect of ovariectomy on d 18 on litter size and maternal performance. In experiment two, no significant line X treatment interactions were found for maternal performance, indicating that both lines responded similarly to ovariectomy. Line L+ showed a positive correlated response in maternal performance. Ovariectomized females had a reduced (P less than .05) number born alive compared with sham-operated females, but the nonsurgically treated females were intermediate.(ABSTRACT TRUNCATED AT 250 WORDS)