Comparison of Intrauterine and Subcutaneous Sites of Estrogen Injection for Luteal Maintenance in Swine1

Intrauterine and subcutaneous sites for estradiol benzoate (EB) injection were compared in 30 gilts to test their relative effectiveness for estrogen-induced maintenance of corpora lutea. Vehicle or EB was injected on d 10 through 14 of the estrous cycle and corpora lutea that were maintained through d 24 were regressed subsequently by exogenous prostaglandin F2 alpha (10 mg). Cycle length (days) was not altered in either subcutaneous (18.6 +/- .5) or intrauterine (19.8 +/- .8) control groups. Gilts receiving 10 mg EB/d sc had longer (P less than .05) cycles (28.6 +/- 2 d) than gilts treated with 100 micrograms EB at either the sc (24.2 +/- 1 d) or intrauterine sites (23.3 +/- 1.3 d). The latter two cycle lengths were longer (P less than .05) than control cycles, but not different from each other. Before d 24, progesterone concentrations (ng/ml serum) were greater (P less than .01) in EB-treated gilts (25.1 +/- 2.0) than in controls (13.0 +/- 2.7). Progesterone concentration patterns were similar between gilts treated at intrauterine or sc sites. Thus, EB-induced maintenance of corpora lutea was not enhanced by direct injection into the uterine lumen.