Effect of gonadotropin administration on estrus synchronization and ovulation rate following induced abortion in swine

Abstract

The objectives of this study were to examine the effects of pregnant mare serum gonadotropin (PMSG) alone or in combination with human chorionic gonadotropin (hCG) on synchronization of estrus and the ovulation rate following prostaglandin F 2α-induced abortion. Twenty-seven pregnant gilts were aborted between Days 20 and 40 of gestation by the administration of PGF 2α (10 mg/injection) at 0700 and 1600 h. Control gilts (C; n = 9) received an injection of physiological saline (2 ml) immediately following the second injection of PGF 2α, while PMSG1 (n = 11) and PMSG2 (n = 7) gilts received an injection of PMSG (1250 IU) from lots #1 and #2, respectively. Gilts which failed to exhibit estrus within 80 h following PMSG were given 500 IU hCG (PMSG1+hCG: n = 5; PMSG2+hCG: n = 4). Gilts were bred at 12 and 24 h after the onset of estrus (Day 0) by natural or artificial insemination. Embryos were recovered between Days 1 and 6 of gestation. Because the source of PMSG had no effect on the interval from PGF 2α to estrus, PMSG1 and PMSG2 gilts were pooled into two groups: PMSG (n = 9) and PMSG+hCG (n = 9). Mean interval from PGF 2α to estrus and its variance were greater for C than PMSG and PMSG+hCG gilts. Mean ovulation rate was greater for PMSG2 as compared with PMSG1 and C gilts (26.0 ± 2.0 vs 15.6 ± 1.6 and 13.2 ± 1.8, respectively). The embryo recovery rate was lower for PMSG2 than for PMSG1 and C gilts. These results indicate that administration of PMSG alone or in conjunction with hCG increases synchronization of estrus following induced abortion. Finally, the ovulatory response to a commercial preparation of PMSG may vary greatly between lots.