Follicular development of canine ovaries stimulated by a combination treatment of eCG and hCG

Abstract

Ovarian follicular dynamics is not well known in dogs. Imaging of ovaries is technically difficult; however, ovaries clamped at a subcutaneous site can more easily be monitored using ultrasound imaging. This study investigated the follicular development of canine ovaries stimulated by hormone treatment using ultrasound imaging of the ovaries clamped at a subcutaneous site. Oestrus was induced using subcutaneous administration of 500 IU equine chorionic gonadotropin (eCG) and 1000 IU human chorionic gonadotropin (hCG) (eCG/hCG). Five bitches were given 1000 IU hCG 11 days after eCG/hCG administration. Examinations with ovarian ultrasonography using a 7.5‐MHz sector transducer, vaginal cytology, and assays of serum oestrogen and progesterone were performed daily until 20 days after eCG/hCG administration. Serosanguineous vaginal discharges and vaginal cytology of two of the bitches were observed. New follicular growth (>1.0 mm in diameter) was observed in all bitches from 2 to 8 days after eCG/hCG administration. The mean diameter of follicles and maximum numbers of follicles per ovary ranged from 2.8 to 5.5 mm and 4 to 16, respectively. The elevation in oestrogen concentrations after eCG/hCG administration was observed in all bitches, and elevation in progesterone concentration (>2 ng mL−1) was observed in three bitches. However, no follicles ovulated until 9 days after hCG administration. In conclusion, although the number of examined bitches were limited, follicular growth in ovaries clamped at a subcutaneous site can be monitored using ultrasound imaging. Ovarian ultrasonography showed that eCG/hCG administration induced new follicular growth and hCG administration induced increases in oestrogen concentrations but not ovulation by hCG administration.

Ultrasonographic observation in combination with progesterone monitoring for detection of ovulation in Labrador Retrievers

“…In this study, the date of ovulation was identified in 93.6% of the initially confirmed follicles. The use of high‐frequency (18 MHz) probe is thought to have contributed to the improved accuracy in this study, whereas 7.5–13 MHz probe was used in previous studies (Renton et al., 1992; Boyd et al., 1993; England &Yeager, 1993; Hayer et al., 1993; Hase et al., 2000; Fontbonne & Malandian, 2006; Bergeron et al., 2013; Domosławska et al., 2014; Hirata et al., 2018). Another factor the accuracy depends on is the operator's experience.…”

“…England and Yeager (1993) suggested that detection of ovulation with ultrasound has limited practical value. Since no method has been established to accurately determine or predict ovulation, ovaries have been surgically clamped at a subcutaneous site for ultrasound imaging to evaluate follicular development (Hirata et al., 2018). It has been reported that pre‐ovulatory follicles in many cases are located very close to each other (Fontbonne & Malandian, 2006).…”

Vaginal stimulation enhances ovulation of queen ovaries treated using a combination of eCG and hCG

“…Bilateral malacotomy of four queens was performed using a ventral‐flank abdominal approach using routine techniques and materials, according to the methods described by Hirata et al (2018). Briefly, the queen was mechanically ventilated with isoflurane in pure oxygen.…”

“…Moreover, ultrasound echogenicity of corpora lutea is variable and depends on the observation period, thus making sonographic detection difficult (Gatel et al., 2020). However, when ovaries are clamped at a subcutaneous site, their follicular growth can more easily be monitored using ultrasound imaging (Hirata et al., 2018). Moreover, the ovarian clamp at the subcutaneous site can provide easy access for repeated collection of oocytes for in vitro fertilization in endangered animals.…”