Selection for ovulation rate in rabbits: Direct and correlated responses estimated with a cryopreserved control population

The aim of this work was to evaluate the response in 10 generations of selection for ovulation rate in rabbits using a cryopreserved control population. Selection was based on the phenotypic value of ovulation rate estimated at d 12 of second gestation by laparoscopy. To produce the control population, embryos from 50 donor females and 18 males, belonging to the base generation of the line selected for ovulation rate, were recovered. A total of 467 embryos (72-h embryos) were vitrified and stored in liquid N-2 for 10 generations. The size of both populations was approximately 10 males and 50 females. The number of records used to analyze the different traits ranged from 99 to 340. Data were analyzed using Bayesian methodology. A difference between the selected and the control populations of 2.1 ova (highest posterior density interval (HPD95%) [1.3, 2.9]) was observed in ovulation rate (OR), but it was not accompanied by a correlated response in litter size (LS; -0.3; HPD95% [-1.1, 0.5]). The number of implanted embryos (IE) increased with selection in 1.0 embryo (HPD95% [-0.6, 2.0]), but this increase was not relevant. Prenatal survival, embryonic survival, and fetal survival (FS) were calculated as LS/OR, IE/OR, and LS/IE, respectively. Prenatal survival was reduced with selection (-0.12; HPD95% [-0.20, -0.04]), basically because of a decrease in FS (-0.12; HPD95% [-0.19, -0.06]). Embryonic survival could have slightly decreased (-0.05; HPD95% [-0.12, 0.02]). In summary, comparison with a control population showed that ovulation rate in rabbits increased with selection without any correlated response in litter size, basically because of a decrease in fetal survival.