In a previous study, the effect of delayed fertilization of ova on the chromosome complement of 6-day blastocysts was investigated (Shaver & Carr, 1969). Human chorionic gonadotrophin (hcg) causes ovulation to occur in rabbits approximately 10 hr after injection. When mating was delayed at least 6 hr, 13% of the blastocysts were found to be triploid. Triploidy was not found in the control series, although blastocysts from animals mated immediately after hcg injection had a 7% incidence of other types of chromosomal anomalies. Rabbits receiving no exogenous gonadotrophin gave rise to only 2% of blastocysts with abnormal chromosomes. This difference led to an experiment in which various doses of hcg were injected before mating in order to determine whether a relationship existed between the dose level and the chromosomal abnormalities found in 6-day blastocysts.
Adult rabbits of mixed breeds purchased from a local supplier were used. Eleven rabbits were