Relationships between components of litter size in unilaterally ovariectomized and intact rabbit does

A study was performed to evaluate the use of unilateral ovariectomy for the measurement of uterine capacity in rabbits through a comparison of the relationships between ovulation rate, number of implanted embryos, and litter size in unilaterally ovariectomized (ULO) and intact does. Data from 211 ULO and 323 intact does were analyzed. The animals were derived from a synthetic line previously selected on litter size. Laparoscopy was performed on all does during their second gestation 12 d after mating and the number of corpora lutea and implantation sites were recorded. Intact and ULO does had the same ovulation rate, confirming the presence of compensatory ovarian hypertrophy in the remaining ovary of the ULO does. The number of implantation sites in the ULO group (11.3) approached the number found in the control group (12.6). Embryonic survival (until implantation) was lower (P < .01) in ULO does (.77) than in intact does (.88), but fetal survival (after implantation) was the same in both groups. The ULO females produced litters 77% of the size of those of the normal control females. Pre- and postimplantation survivals were not related in intact does but seemed to be related in ULO does through an effect on the number of implantation sites. The coefficient of the regression of number of implantation sites on ovulation rate was positive in control does (.62 +/- .06) and was also positive in ULO does (.31 +/- .07), showing that a higher ovulation rate would have resulted in a higher number of embryos being implanted in both groups. Litter size had a positive coefficient of regression on number of implanted embryos in both control does (.67 +/- .04) and in ULO does (.49 +/- .05), showing that a higher number of implantation sites would have produced a higher litter size in both groups. Overall, however, the regression of litter size on ovulation rate was positive in control does (.30 + .06), but not significantly different from zero in ULO does (.07 + .08), indicating that unilateral ovariectomy had the desired effect of making litter size independent of ovulation rate.