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Production of Estradiol by each Ovary during the Estrous Cycle of Cows^1,2,

Michigan State University⁵, East Lansing 48824-1255

Abstract

The objective of our experiment was to examine changes in serum concentrations of estradiol in each utero-ovarian vein before, during and after gonadotropin surges. Four cows were given prostaglandin F₂ (PGF₂) during diestrus and three cows were allowed to cycle spontaneously. All cows had a cannula in each utero-ovarian vein and in one jugular vein. Most cows had two transient rises in estradiol, primarily coming from a single ovary, preceding and after luteinizing hormone (LH) surges. The first rise in estradiol began after luteal regression and was sustained from 48 h before a preovulatory LH surge to the end of the LH surge. The second rise in estradiol was sustained from 72 to 168 h after the end of an LH surge. To determine how rapidly asymmetrical production of estradiol began during luteolysis, several cows were injected with PGF₂ during the luteal phase. Blood samples were taken from a jugular and both utero-ovarian veins at hourly intervals before and after PGF₂. Asymmetrical production of estradiol began within 3 h after an injection of PGF₂. We concluded: (1) that a single ovary was responsible for the sustained increases in concentration of estradiol that occur during proestrus to estrus and early diestrus in cows and (2) that cows may have at least one follicle capable of producing estradiol during most days of an estrous cycle, thus little delay in selection of which follicle eventually ovulates occurs after luteal regression.

¹ This manuscript was published with permission of the Director of the Michigan State Agr. Exp. Sta. as journal article No. 10700.

² We gratefully acknowledge Larry Chapin for assistance in computer analysis and members of the Large Animal Reproduction Laboratory, especially Don Kinsley, for their assistance in collection of blood samples. This research was supported by NSF Grant PC 7904571.

³ To whom reprint requests should be addressed. Telephone no. (517) 353-8777.

⁴ Present address: School of Vet. Med., North Carolina State Univ., Raleigh 27650.

⁵ Depts. of Anim. Sci. and Large Animal Surgery and Medicine.