Sex ratio in rabbits following modified artificial insemination

The possibility of modifying the sex ratio of rabbit litters was examined in two experiments involving artificial insemination (AI) with fresh semen. Three time periods of AI, relative to ovulation, were used in Experiment 1: (a) control, GnRH was administered immediately after AI with ovulation estimated to occur 10-12 h after AI; (b) early AI, GnRH was given 6 h after AI so that ovulation was delayed until 16-18 h after AI; (c) late AI, GnRH was administered 6 h before AI, which was performed 4-6 h before ovulation. There were 13 does per treatment, and each doe was used in the same treatment for three AIs at 42-day intervals. The second experiment involved two treatments in which the does were inseminated as for the control in Experiment 1 and AI was performed using semen prepared in the normal manner (Treatment 1) or after centrifugation through 11 discontinuous Percoll gradients (Treatment 2). There were 20 does per treatment, and each doe was used in the same treatment for three AIs at 42-day intervals. The proportion of female kits produced in Experiment 1 was: control 41.7 ± 19.1%, early AI 49.8 ± 17.8%, and late AI 41.4 ± 16.4%. These proportions did not differ significantly between treatments or from the expected 50:50 sex ratio. Fertility was reduced by the early (60.0%) and late (73.7%) AI treatments relative to control AI (80.0%), and the difference between early and control AI almost achieved statistical significance (P < 0.07). In Experiment 2, the proportion of female kits was not affected by treatment (control, 51.1%; Percoll, 54.8%), and there was a similar level of fertility for both treatments (control, 76.0%; Percoll, 74.1%). Prolificacy and perinatal mortality were not affected by treatment in either experiment. It was concluded that neither the timing of insemination nor Percoll centrifugation of semen affected the sex ratio at birth of rabbit litters.