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Effect of Estrogen on Luteal Function in Prepuberal Gilts¹

University of Georgia², Athens 30602 and and Richard B. Russell Research Center, ARS, USDA, Athens 30601

Abstract

The effect of estrogen on the luteotropic-luteolytic mechanism of prepuberal gilts, 120 to 130 days of age, was studied following induced ovulation with 1,000 IU Pregnant Mare Serum Gonadotropin (PSMG) and 500 IU Human Chorionic Gonadotropin (HCG). Control gilts were artificially inseminated on Day 0 (Day following HCG=Day 0). With the exception of the bred controls in Experiment 2, the corpora lutea (CL) of all gilts were marked with sterile charcoal on Day 6 to 9. Daily intramuscular injections of estradiol benzoate (EB) in corn oil or corn oil vehicle were given from Day 10 through Day 15. Plasma progestin concentrations were determined by radioimmunoassay to assess luteal function. In Experiment 1, eight bred control gilts received corn oil, 10 gilts received 5 mg EB and eight gilts received 10 mg EB. In Experiment 2, five control gilts were bred. The remaining gilts were hysterectomized on Day 6 to 9 with six gilts receiving corn oil and five gilts each receiving either 5 or 10 mg EB.

In Experiment 1, only one control gilt was pregnant on Day 26. None of the gilts receiving either 5 mg or 10 mg EB had maintained CL on Day 26. In Experiment 2, none of the bred control gilts were pregnant on Day 30. Of the hysterectomized gilts, all gilts which received corn oil had functional CL on Day 30. Three gilts which received 5 mg EB and all gilts which received 10 mg EB failed to maintain CL. Unlike the mature gilt, EB appears to inhibit luteotropic support sufficiently to cause luteal regression in prepuberal gilts and because of this, it is not possible to determine whether EB blocks the luteolytic effect of the non-gravid uterus as it does in the mature gilt.

¹ The authors gratefully acknowledge Ms. E. Paige Jordan, Mr. Bennett Johnson and Mr. Tony A. Puglisi for their technical assistance.

² Department of Animal and Dairy Science.

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