Fate of the dominant follicle, embryonal survival, and pregnancy rates in dairy cattle treated with prostaglandin F-2 alpha and progestins in the absence or presence of a functional corpus luteum

Our objective was to examine the role of progestin type on serum concentrations of progesterone (P-4) and estradiol-17 beta (E(2)), ovarian follicular dynamics, and fertility in cattle in the presence or absence of a corpus luteum (CL) in an estrus synchronization scheme using progestin and PGF(2 alpha). In Exp. 1, 325 cows and heifers were given one injection of PGF(2 alpha) (d 0) and then assigned randomly within parity to five treatments: to receive a second PGF(2 alpha) injection 14 d later (control); to receive norgestomet (NORG) for 7 d beginning on d 8, with a second PGF(2 alpha), injection given either 1 d (NORG + no CL) or 6 d (NORG + CL) after insertion; or to receive a P-4-releasing intravaginal device (PRID) in lieu of norgestomet at comparable times. Presence or absence of a CL was based on concentrations of serum P-4 on d 14. Pregnancy rates after insemination were greater (P < .01) with luteal treatments than with nonluteal treatments. Embryonal survival between two stages of pregnancy was 87.6%. In Exp. 2, ovarian structures in 50 cows were examined daily using ultrasonography and the same five treatments. Diameter of the ovulatory follicle was greater (P < .05) with the nonluteal treatments (NORG and PRID + no CL) than with the control and luteal treatments (PRID and NORG + CL). Replacement of the dominant follicle during progestin treatment was altered by treatment (luteal status) and stage of the estrous cycle. Fertility was not enhanced by exogenous progestins when a CL was present. In the absence of a CL, progestin (P-4 less than NORG at the doses used) reduced fertility by increasing E(2) and the diameter of the ovulatory follicle and decreasing turnover of dominant follicles.