Effect of altering the intervals between consecutive superovulatory doses of porcine follicle-stimulating hormone on ovarian responses and embryo yields in anestrous ewes

The effect of varying intervals between successive gonadotropin injections on the superovulatory outcomes in anestrous Rideau Arcott ewes superstimulated for ovarian follicular development with multiple doses of porcine FSH (pFSH) was evaluated in a single study. Twenty-five animals received six (1 × 2.5 ml and 5 × 1.25 ml) injections of Folltropin®-V given at 0800 and 1600 h or at 0800 and 2000 h in Group 1 (n = 9) or Group 2 (n = 16), respectively. An i.m. injection of 500 IU of equine chorionic gonadotropin (eCG; Folligon®) was given concurrently with the first pFSH dose. Time of estrus was synchronized among ewes with intravaginal sponges containing 60 mg of medroxyprogesterone acetate (Veramix®) that were left in place for 14 days; sponges were removed at the time of the 5th pFSH injection. Six days after insertion of MAP sponges, all ewes received an i.m. injection of estradiol-17β dissolved in 1 ml of sesame oil (350 μg/ewe) to synchronize follicular wave emergence. Following the last pFSH dose, all animals were given a single i.m. injection of 50 μg of gonadotropin-releasing hormone (GnRH; Cystorelin®) to induce ovulations before placing in a pen with four fertile rams for 36 h. The ovarian responses were assessed and embryos recovered surgically 7 days after GnRH injections. The mean number of corpora lutea was greater (P < 0.05) in Group 1 compared with Group 2 ewes (21.0 ± 2.9 compared with 10.4 ± 1.6, respectively; mean ± SEM) but there was no difference (P > 0.05) in the number of transferable embryos (5.4 ± 2.4 compared with 5.4 ± 1.3/ewe, respectively), and Group 1 animals had significantly more degenerated embryos than Group 2 ewes (2.6 ± 1.2 compared with 0.6 ± 0.3/ewe, respectively). A superovulatory protocol wherein pFSH injections were given at 0800 and 1600 h was more effective in terms of inducing multiple ovulations than the protocol with 12-h intervals between consecutive pFSH doses, but it was not associated with an increased production of transferable quality embryos by anestrous ewes.