1. Department of Obstetrics, Gynaecology and Reproduction; Faculty of Veterinary Science; Chulalongkorn University; Bangkok 10330 Thailand
2. Department of Veterinary Technology; Faculty of Veterinary Technology; Kasetsart University; Bangkok 10900 Thailand
3. Department of Anatomy; Faculty of Veterinary Science; Chulalongkorn University; Bangkok 10330 Thailand