Ultrasonographic monitoring of follicular development, ovulation and the early luteal phase in the bitch.

Follicular development, ovulation and the early luteal phase in 15 oestrous cycles of 13 individual bitches were monitored daily by ultrasonography using a 7.5 MHz sector scanner transducer. These findings were compared with vaginal cytology and changes in the peripheral plasma concentrations of oestradiol, luteinizing hormone (LH) and progesterone. Both ovaries were imaged throughout the period of study. Follicles were identified as anechoic spherical structures as early as day 1 of pro-oestrus in two cases and on days 3-4 in 13 cases. The average follicular size increased from 3.7 +/- 0.6 mm to 6.9 +/- 0.7 mm (P < 0.001) between day -5 and the LH surge (day 0). The anechoic structures then increased in size to 7.5 +/- 0.7 mm (P < 0.05) until day 2 after the LH surge; their diameters continued to increase during corpus luteum development, up to 8.1 +/- 0.6 mm (P < 0.001) on the first day of dioestrus. The average number of follicles counted imaged on the day of the LH surge was 3.3 +/- 0.4 on the left ovary and 3.7 +/- 0.7 on the right ovary. The rapid disappearance of the anechoic antrum, corresponding to ovulation, was detected in only two bitches. In the remaining cases follicular rupture was not detected; however, starting at the LH surge, a gradual thickening of the antral wall occurred. This corresponded to a progressive obliteration of the anechoic region and was characteristic of the postovulatory corpora lutea. These changes led to a significant decrease (P < 0.05) in the number of anechoic structures to 2.4 +/- 0.5 on the left ovary and 3.3 +/- 0.5 on the right ovary by day 1 of dioestrus. During the follicular phase, the mean increase in oestradiol concentration was correlated with follicular size (P < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)