This study aimed to evaluate the effects of slaughter time (after 24 or 72 hours from matting) on ovarian and genital characteristics of superovulated female rabbits and quality and recovery rate of embryos. A total of 38 New Zealand White rabbit females were used in this study. All females were non-parous averaging 5 months of age and ranging between 2.7-2.9 kg LBW. All animals were superovulated by i.m. injection with 150 IU PMSG (Foligon), followed by 75 IU HCG (Pregnyl) at the time of natural mating (72 h after PMSG injection). All treated females were slaughtered either 24 (G1, n=18) or 72 (G2, n=20) hours after mating, where ovaries and reproductive tract of each female were separated to determine weight and length of the ovary, oviduct and uterus as well as number of follicles and corpora lutea (CL) on the ovarian surface. Embryos were collected from superovulated does in both groups Embryos were recovered from uterine horns by flushing with phosphate buffer solution with 10% fetal calf serum at room temperature (20-25 oC). Thereafter, the recovered embryos were counted and examined for different embryo stages using an inverted microscope fitted with a calibrated eye piece micrometer reflected on stereo-microscope. Results show that absolute ovarian weight increased (P>0.01) by 56% (0.26 vs. 0.41 g), ovarian weight relative to LBW increased (P<0.01) by 66.6% (0.09 vs. 0.15 g/kg) and ovarian length increased (P<0.05) by 18.5% (1.31 vs. 1.55 cm) in G2 compared with G1. Number of follicles/ovary did not differ between G1 and G2. However, number of CL/ovary increased (P<0.001) in G2 than in G1(6.4 vs. 8.2/ovary). There were insignificant differences in absolute weight, relative weight to LBW and length of both oviduct and uterus between G1 and G2. Number of embryos recovered per ovary was nearly similar in G1 and G2 (4.30 and 4.35/ovary). However, recovery rate was higher (P>0.01) in G1 than in G2 (66.7 vs. 53%). The highest distribution of embryos in G1 was recorded in 2-cell stage (zygote, 84.4%), followed by 5.2% in 4-cell stage, while 10.4% were in abnormal type vs. 84% in compacted morula stage, 3.4% in early morula stage, 2.9% in early blastocyst stage and 9.8 in abnormal type.
The current study may conclude that rabbit does should be superovulated by PMSG and HCG and slaughtered after 24 h of mating when embryos at early stage are needed for banking females of high genetic merit, and slaughtered after 72 h of mating if embryos at morula stage were needed for embryo transfer.