ULTRASONOGRAPHY AND ENDOCRINOLOGY OF OVARIAN DYSFUNCTIONS INDUCED IN HEIFERS WITH ESTRADIOL VALERATE

This study monitored the long-term follicular dynamics and changes in ovarian steroid hormones associated with an experimental model of cystic ovarian degeneration (GOD) in the heifer. In the treated group (n=7), Holstein heifers received a single injection of 500 mu g of cloprostenol (prostaglandin F2(a), PG) and 5 mg of estradiol valerate (EV) on either Day 17, 18 or 19 of the estrous cycle. The control group (n=7) received only PG. Transrectal ultrasound was performed daily, beginning 8 to 10 d before injection and continuing until a return to normal cyclicity (40 to 74 d). Blood samples were taken twice daily over the same period. The EV disrupted the normal follicular development as well as the plasma progesterone and estradiol profiles of 6/7 heifers in the treated group. Two different types of responses were observed. The Type-I response (n=2) was characterized by a premature ovulation followed by a corpus luteum (CL) which persisted for over 30 d. The Type-II response (n=4) was characterized by anovulation followed by the emergence of a large ovarian structure which could further be subtyped. In Type- IIA (n=2), this follicle ovulated at an exaggerated size of 19 or 24 mm (mean diameter of controls: 13.4 +/- 2.7 mm). The subsequent cavernous CL was very large at 35 and 37 mm (mean diameter of CL in controls: 23.8 +/- 2.0 mm). In Type- IIB (n=1), the follicle present at the time of injection continued to grow and became a luteinized cyst. In Type-IIC (n=1), several waves of follicular cysts developed and persisted for 52 d. This study suggests that EV induces a range of ovarian dysfunctions including different forms of GOD. The individual differences in the stage of folliculogenesis at the time of injection of EV may be responsible for the different types of responses.