Restoring ovulation in beef donor cows with ovarian cysts by progesterone-releasing intravaginal silastic devices

The objective of this study was to determine the efficacy of a progesterone -releasing intravaginal silastic device (Controlled Internal Drug Release: CIDR) for inducing ovulation in beef cows with persistent ovarian cysts. Fi fteen cows with cysts and abnormal cycles for over 40 days were randomly as signed to receive either a single CIDR (CIDR group, n=9), or a CIDR contain ing no progesterone (blank CIDR) (BLANK group, n=6) for about 14 days. Dete rmination of plasma progesterone levels at the beginning of CIDR treatment indicated 4 of 6 BLANK cows with non-luteinized cysts and 5 of 9 CIDR cows with non-luteinized cysts. In 5 of 6 BLANK cows, one follicular wave appeared and newly emerged domina nt follicles increased in size up to 20 mm in diameter and persisted during the experiment, while one cow experienced estrus with spontaneous ovulatio n. In contrast, during CIDR treatment, 2 or 3 waves, in which dominant foll icles were from 7 to 15 mm in diameter, appeared approximately at 7-day int ervals. Within 3 days after CIDR removal, estrous behavior was detected fol lowed bq ovulation of the dominant follicle in the last wave. All CIDR cows resumed normal cyclicity with 3 follicular waves for over 2 months. Insert ion of a CIDR caused a rapid increase of about 2 ng/mL in plasma progestero ne. The levels were greater than 1.3 ng/mL until removal of a CIDR, then dr opped under 0.3 ng/mL. Concentrations of plasma estradiol in BLANK cows inc reased during growth of the cystic follicles, with high levels greater than 10 pg/mL for over 10 days. In 4 of 5 cows with non-luteinized cysts, with high plasma estradiol on the day of CIDR insertion, CIDR treatment resulted in rapid decline of estradiol levels. During placement of the CIDR, estrad iol levels showed no increase in the growth phase of a newly appeared domin ant follicle. After CIDR removal, however, estradiol significantly increase d associated with the growth of ovulatory follicles in all 9 cows. A transi ent increase in plasma FSH levels preceded detection of each follicular or cyst wave in both BLANK and CIDR cows. Pulse frequency and mean concentrati on of LII in cows with nonluteinized cysts showed values corresponding to t hose in normal follicular phase. However. throughout CIDR treatment, these parameters reduced to levels found in the normal luteal phase. In cows with luteinized cysts, parameters of LH secretion were as low as in the normal luteal phase before and during CIDR treatment, then increased significantly after CIDR removal. present results indicate that treatment with CIDR prov ed effective in restoring ovulation and reestablishing: normal cyclicity in beef donor cows with cysts persistent for a lent: period. The CIDR reduced and maintained LH secretion at normal luteal levels, thereby, inducing atr esia of estrogen-active cysts and preventing formation of cysts from the ne wly emerged follicles. (C) 2001 by Elsevier Science Inc.