To identify the time and characteristics of ovulation, 5 bitches were evaluated during heat by ultrasonography , laparoscopy and hormonal assays. Blood collections for progesterone and oestradiol 17-f3 assays and ultrasonography were performed every day and laparoscopy every other day. At ultrasonography, ovaries appeared as anechoic structures about 5 days before the estimated LH peak and gradually increased in size. The greatest changes were observed between days 2 and 4 post-LH peak: echogenicity varied greatly from one animal to another and from one day to the following going from totally anechoic to mixed hypo and hyperechogenicity. Then from day 6, ovaries always appeared as hypoechoic structures assimilated to corpora lutea. At laparoscopy , small follicles were seen as early as day 10 before the LH peak. Their size slowly increased to become large protubering follicles around the day of LH peak (day 0). At day 1, corpora lutea were observed for the first time and were present in all animals by day 5. During that period preceeding day 5, some ovaries had both corpora lutea and follicles clearly visible on their surface. In one animal, haemorrhagic foci were observed at day 3. Neither ultrasonography, nor laparoscopy allowed precise determination of the time of ovulation. Indeed, follicle collapses was never observed, but changes in echogenicity and in the appearance of the ovaries observed by laparoscopy, suggested that ovulation occurred between days 2 and 4 when progesterone concentrations were 12.6 f 6.2 and 32.1 f 10.9 nmollL, respectively. Veterinary Radiology (519) 823-8800, extension 4000, FAX#: (519) 767-031 1, and provide a current curriculum vitae and the names of at least three referees.
