PARENT SESSION
Follicular Development

ULTRASOUND AND ENDOCRINE EVALUATION OF THE OVARIAN RESPONSE TO A 12-DAY (D) MEDROXYPROGESTERONE (MAP) SPONGE AND SINGLE INJECTION OF PREGNANT MARE SERUM GONADOTROPIN (PMSG) IN EWES IN SEASONAL ANESTROUS.

Barrett, David¹, Bartlewski, Pawel², Rawlings, Norman¹, ^{1 2}

ABSTRACT- Five hundred IU of PMSG is commonly given to anestrous ewes, at the end of a 12- to 14-d treatment with progestogen impregnated intravaginal sponges, to synchronize estrus and induce ovulation. If PMSG is omitted very few ewes ovulate. The exact way in which PMSG affects the waves of antral follicle growth to effectively stimulate ovulation in anestrous ewes is not known. Twelve seasonally anestrous Western White Face ewes were treated for 12 d with progestogen sponges (60 mg; Veramix®, Upjohn) and six ewes were given PMSG (500 IU; i.m.) on the day of sponge removal. Ultrasound scanning and blood sampling started 7 d prior to sponge insertion and ended 10 d (scanning) or 20 d (blood sampling) after the removal of sponges. PMSG treatment did not result in any changes in follicle numbers, size, or growth characteristics of all follicles ≥ 3mm in size (P>0.05). All ewes treated with PMSG but only one of the six control ewes ovulated. Mean ovulation rate for the PMSG treated ewes was 2.3±0.3 (range: 1 to 3). Three ewes ovulated follicles from the last 2, one ewe from the last, and two ewes from the penultimate follicle waves before PMSG. The number of ovulations per ewe from the last and penultimate waves emerging before PMSG was 1.2±0.3 and 1.0±0.4, respectively. Luteal structures were seen in all PMSG treated sheep but none of the control sheep. The mean number of CL observed was 2.2±0.3 (range: 1 to 3). The inter peak interval for FSH pulses was longer in ewes given PMSG (3.8±0.3 d) compared to control ewes (2.8±0.2 d) after sponge removal (P<0.01). When serum estradiol concentrations were analyzed over the entire study period, there was a significant interaction between treatment group and day of experiment; on days 1, 3, and 4 after ovulation, serum concentrations of estradiol were higher in PMSG treated ewes compared to control ewes (P<0.05). We concluded that 500 IU of PMSG given at the end of a 12-d period of treatment with progestogen impregnated intravaginal sponges does not alter antral follicle numbers, size, or growth characteristics; it recruits follicles to ovulate from the last 2 waves of follicles before treatment and results in increased serum concentrations of estradiol for several days after ovulation.

KEY WORDS: seasonal anestrous, medroxyprogesterone (MAP), PMSG, ewes