215 DELETERIOUS EFFECTS OF PROGESTAGEN TREATMENT ON FUNCTIONALITY OF PREOVULATORY FOLLICLES IN SHEEP
Authors: Letelier C. , García-Fernández R. A. , García-García R. M. , Arias-Álvarez M. , Contreras-Solis I. , Sanchez M. A. , Ratto M. , Flores J. M. , Gonzalez-Bulnes A. 
Published: August 2010

The use of progestagen for 14 days in protocols for estrus synchronization has been reported to affect conception rate in sheep. We evaluated the effects of progestagen treatment on the growth pattern and follicular function of preovulatory follicles (PF) and their implication for subordinated follicles (SF). Adult female sheep were randomly assigned to the following estrus synchronization groups: 1) FGA (n = 7), which received an intravaginal device of fluorogestone acetate sponges (Chronogest®, Intervet International, Boxmeer, the Netherlands) for 14 days, or 2) PGF (n = 7), which received 3 i.m. administrations of 125 μg of cloprostenol (Estrumate®, Mallinckrodt Vet GmbH, Friesoythe, Germany) 10 days apart. The third cloprostenol administration in the PGF group was given at the same time of sponge withdrawal in the FGA group (Day 0 = day of sponge withdrawal). Ultrasonographic examinations of the ovaries for assessment of follicular development were carried out daily from Days 0 to 2 by using a scanner (Aloka SSD500) equipped with a 7.5-MHz transducer adapted for transrectal examinations. Follicular function was evaluated in terms of estradiol secretion, and blood samples were taken every 12 h to determine plasma estradiol concentration from Days 0 to 2. Ovaries from all females in both groups were recovered by ovariectomy on Day 2 to determine apoptosis by immunohistochemistry for active caspase-3 in granulosa cells from SF of 3 to 5 mm in diameter. Additionally, SF were histologically classified as healthy, early, or advanced atretic. Data were analyzed by Student t-test and Pearson correlation. The total number of PF observed on Day 2 was 15 and 12 for the PGF and FGA groups, respectively. The 90.9 and 93.3% of PF recorded in the PGF and FGA groups, respectively, on Day 2 was retrospectively identified on Day 0. The 33.6 and 46.6% of those follicles from the PGF and FGA groups, respectively, corresponded to follicles >5 mm in diameter. Although mean diameter of PF was higher in the FGA group than in the PGF group (5.4 ± 0.4 mm v. 4.5 ± 0.4 mm, respectively; P < 0.01) on Day 0, PF diameter was similar between groups on Day 2. Plasma estradiol concentration was significantly higher (P < 0.05) in the PGF group on Day 1 (3.1 ± 0.2 pg/mL v. 1.7 ± 0.2 pg/mL in the FGA group) but did not differ between groups on Day 2. The growing pattern of the PF in the PGF group significantly (P < 0.05) affected the total number of SF, and there was a tendency (P = 0.08) for an increase of the total number of healthy follicles in the same group. In addition, advanced atretic follicles from the FGA group were significantly higher than those observed in the PGF group (P < 0.001). Additionally, caspase-3 immunoreactivity was higher in the FGA group than in the PGF group (P < 0.05) and it was associated with the largest SF in both groups. All of these finding are indicative of the presence of aged follicles with an extended permanence in the ovary. We concluded that the use of progestagen for 14 days in protocols for estrus synchronization in sheep affects the growth pattern and functionality of the preovulatory follicle during the follicular phase and may have a deleterious consequence on oocyte competence.

CYCITAGL2005-02669 and DID-D-2007-03 UACh.