Superovulatory and embryo yielding in sheep using increased exposure time to progesterone associated with a GnRH agonist

• We examine prolonged exposure to progesterone in superovulation protocol.
• We examine prolonged exposure to progesterone plus GnRH in superovulation protocol.
• Longer progesterone exposure tended to reduce the degenerate embryos rate.
• Longer progesterone exposure plus GnRH administration increased fertilization rate.

Response to superovulatory, embryo yields and quality, were evaluated after increasing exposure time to exogenous progesterone during superstimulation, with or without the addition of a GnRH agonist. Thirty-four ewes from the Santa Inês breed were synchronized with an intravaginal progesterone device (CIDR). The animals were randomly divided into three groups: exposure to progesterone for 14 days (Control, n = 12); 12 h extension of progesterone exposure (12hP4 group, n = 11); and 12 h extension, associated with the administration of 25 μg of gonadorelin acetate (12hP4GnRH group, n = 11). From the 12th to the 15th day of protocol, 133 mg of pFSH were administered through eight decreasing doses. Artificial inseminations were performed 36 and 48 h after device withdrawal, using frozen/thawed semen. The number of ewes on estrus and the time to onset of estrus after withdrawing device were similar among between all groups (P > 0.05). All groups presented high superstimulatory response (averages ranging from 14.33 to 16.18 follicles ≥4 mm) (P > 0.05). All groups also showed a large quantity of CL (averages ranging from 11 to 12) (P > 0.05). The longer exposure to progesterone no reduced degenerated embryo proportion (Control = 30%; 12hP4 = 7% and 12hP4GnRH = 10%; P > 0.05). The fertilization rate was significantly higher in 12hP4GnRH when compared to Control and to 12hP4 (77%, 34% and 41% respectively). These results suggest the association of longer progesterone exposure plus GnRH administration is an alternative to increase oocyte fertilization rates when fixed time insemination is used.