Inhibition of Pregnancy with Indomethacin in Mature Guts and Prepuberal Guts Induced to Ovulate

Twenty prepuberal (P) gilts, 56.5 ± 1.1 kg body weight, were induced to ovulate with 1000 IU of pregnant mare’s serum gonadotropin followed 72 h later by 500 IU of human chorionic gonadotropin (hCG), and bred by artificial insemination (AI) with 50 ml fresh pooled boar semen the day after hCG treatment (Day 0). Eighteen mature (M) gilts, 120.6 ± 1.7 kg body weight, were bred by AI each day of estrus using pooled semen from the same boars (onset of estrus = Day 0). One-half of each group was fed the prostaglandin (PG) synthesis inhibitor indomethacin (IND), at 10 mg/kg body weight, or control (C) feed twice daily on Days 10 to 25. Blood samples taken by venipuncture on Days 10, 15, 20 and 25 were quantitated for progesterone (P4) and 13,14-dihydro-15-keto-PGF2 α (PGFM) by radioimmunoassay. Ovaries were examined on Day 26. All M-C gilts were pregnant, whereas 3 of 9 M-IND gilts (P<0.05) and none of the P gilts (P<0.01) were pregnant. Three of the 6 nonpregnant M-IND gilts displayed estrus on Day 21. The 3 remaining M-IND gilts had maintained corpora lutea (CL) on Day 26. Only corpora albicantia were present in P gilts on Day 26. Serum P4 concentrations for M-C gilts, nonpregnant M-IND gilts with maintained CL, and pregnant M-IND gilts were not different. Serum P4 for all nonpregnant gilts in which CL had regressed by Day 25 decreased to less than 5 ng/ml on Day 20. Serum PGFM concentrations on Days 15, 20 and 25 demonstrated that IND blocked PG synthesis. Therefore, inhibition of PG secretion failed to protect CL from the luteolytic influence of the uterus and failed to allow maintenance of pregnancy in P gilts. Pregnancy failure in 6 of 9 M-IND gifts indicates that PG production may be essential for establishment of pregnancy