Induced prostaglandin release alters steroid concentrations but not pregnancy survival in cows.
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Embryonic mortality (EM) is a major factor limiting reproductive efficiency in cattle, and despite negative connotations related to reproductive performance, prostaglandin F2 (PGF2) is capable of being released by the uterus by Day 30 of gestation. Therefore, the objective was to evaluate differences in PGF2 release after an oxytocin challenge between cows with high circulating concentrations of pregnancy-associated glycoproteins (PAGs) vs low PAG because of the association of increased PAG concentrations with pregnancy success. At Day 30 of gestation, pregnant cows were divided into oxytocin treatment (OT; n = 13) and control (CON; n = 12) groups. Treatment cows were further subdivided by circulating PAG concentration (high PAG, n = 7; and low PAG, n = 6). Blood samples were collected every 30min beginning 1h before oxytocin administration and continuing for 4h. Prostaglandin F2 metabolite (PGFM), progesterone, estradiol-17 (E2), and PAG concentrations were quantified. The peak concentration of PGFM occurred 2h after oxytocin injection in treatment animals and returned to baseline levels by 4h. No correlations were observed between PAG and PGFM, progesterone, or E2 concentrations (P > 0.05). There was no difference in initial or final PGFM concentrations between groups (P > 0.05). Progesterone and E2 concentrations decreased in cows after treatment of oxytocin (P < 0.05); however, only progesterone returned to basal concentrations by the end of the sampling period. In summary, cows with high vs low PAG concentrations at Day 30 of gestation have a similar PGFM response to oxytocin challenge.