The aim of the present study was to investigate the ovulation rate and its relationship to fertilization ability in Landrace, Durock and Crossbred pigs. Gilts were natural mated at a body weight of at least 120 kg under the same hormone treatment. Embryos were surgically collected 1 day after natural mating (Day 0). Embryos derived from in vivo-fertilized oocytes were cultured in medium PZM-3. The ovaries were examined and the pathological findings were recorded. The number of corpus hemorrhagicum was counted, and was assumed to equal the ovulation rate. There was no difference in the number of corpus hemorrhagicum (20.4, 28.8 and 23.2) and ovulation (13.5, 26.8 and 17.2) in the Landrace, Durock and Crossbred pigs. The two pronucleus formation was 76.0, 80.0 and 86.9%. The Day-7 embryos had blastocyst rates of 68.0, 75.0 and 73.9%. There was no difference in the number of total cells and apoptotic cells. In the future, more studies require determining relationships between ovulation and fertilization rate in different species of pigs.

• Hye-Ryung Yoon(Animal Biotechnology Division, National Institute of Animal Science, RDA, Jeollabuk-do 55365)
• Hak-Jae Chung(Animal Biotechnology Division, National Institute of Animal Science, RDA, Jeollabuk-do 55365)
• Kyong-Woon Kim(Animal Biotechnology Division, National Institute of Animal Science, RDA, Jeollabuk-do 55365)
• Sung June Byun(Animal Biotechnology Division, National Institute of Animal Science, RDA, Jeollabuk-do 55365)
• Mi-Ryung Park(Animal Biotechnology Division, National Institute of Animal Science, RDA, Jeollabuk-do 55365)