Hamsters were assigned to one of three groups: 1) control; 2) superovulated with PMS on Day 1 of estrous cycle with hCG treatment 52 h later; and 3) superovulated with PMS on Day 1 of estrous cycle with hCG treatment 76 h later. The time of ovulation was not different between groups. The ovulation rate in groups 1, 2, and 3 was 1.27 ± 0.6, 53.2 ± 3.7, and 58.9 ± 6.1, respectively. The percentages of fertilization in mated animals were 94.7, 35.1, and 89.8, respectively, for the three groups. In group 2 the fertilization rate was significantly lower (P<0.005) than in the other two groups.

Artificial insemination of group 2 animals resulted in a fertilization rate of 56.7%. The proportion of oocytes with attached or penetrating spermatozoa was also lower in group 2. Chromosomal abrerration of ovulated oocytes was not different between groups. From these results, we conclude that administration of hCG to superovulated hamsters as long as 76 h after PMS treatment results in increased fertilization with no adverse effect on oocyte normality.