Effect of estrogen formulation and its site of deposition on serum PGFM concentrations, uterine contractility, and time of ovulation in artificially inseminated weaned sows.

At the time of artificial insemination, 48 mixed parity sows were assigned by parity to receive 25 microg estradiol-17beta either in oil deposited onto the vaginal mucosa (E-oil), or dissolved in extended semen (E-semen), or received no estrogen and served as controls. All sows were inseminated transcervically 24 h after detection of estrus. The time of ovulation was determined in 15 sows per treatment by transrectal ultrasonography. Concentrations of prostaglandin F2alpha metabolite (PGFM) were determined in blood samples obtained from eight sows per treatment at 1 h intervals from 1 h pre-treatment until 7 h post-treatment. The remaining eight sows per treatment were fitted with a transducer to allow determination of intrauterine pressure changes during 1 h pre-treatment until 5 h post-treatment. There were no differences among treatments for wean to estrus interval, size of ovarian follicles at the time of treatment or the estrus detection to ovulation interval. In all treatments, plasma PGFM concentrations were increased from 1 h after treatment. However, the increase was greater and of longer duration in the E-oil sows (P=0.03) supporting the suggestion that this formulation and route of administration enhanced uterine PGF2alpha release. Compared to controls, both estradiol treatments were associated with myometrial contractions of increased amplitude and duration, supporting a causal link between estradiol treatment, increased uterine PGF2alpha release, and enhanced myometrial contractility.