Exogenous Progesterone and Progestins as Used in Estrous Synchrony Regimens do not Mimic the Corpus Luteum in Regulation of Luteinizing Hormone and 17β-Estradiol in Circulation of Cows1

Abstract

Our working hypothesis was that the low concentrations of progesterone (P4) and synthetic progestins administered in hormonal regimens to control estrous cycles of cows would have similar effects on secretion of LH and 17 beta-estradiol (E2). In addition, we hypothesized that concentrations of exogenous P4 typical of the midluteal phase of the estrous cycle and the corpus luteum (CL) would have similar effects on LH and E2, and the effects would be different from those of synthetic progestins and low concentrations of P4. Cows (n = 29) were randomly assigned to one of five treatment groups: 1) one Progesterone Releasing Intravaginal Device (1PRID; n = 6); 2) two PRIDs (2PRID; n = 6); 3) norgestomet, as in Syncro-Mate-B regimen (SMB; n = 6); 4) melengestrol acetate (MGA; 0.5 mg/day; n = 5); and 5) control (CONT; n = 6). Treatments were administered for 9 days (Day 0 = initiation of treatment). All cows from 1PRID, 2PRID, SMB, and MGA groups were injected with prostaglandin F2 alpha (PGF2 alpha) on Days 2 and 5 of the treatment period to regress CL. Cows in the 1PRID and SMB groups were also administered exogenous estrogen according to the respective estrous synchronization protocol for these products. Daily blood samples were collected from Day 0 to 35 to determine concentrations of P4. On Day 8, blood samples were collected at 15-min intervals for 24 h to determine pattern of LH secretion. On Day 9, all treatments ceased and cows in the CONT group received injections of PGF2 alpha.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of the ovulatory follicle diameter and progesterone concentration on the pregnancy rate of fixed-time inseminated lactating beef cows

“…Unfortunately, the authors of the present study were not able to perform daily ultrasound examination in all cows to ensure that the very large follicles detected were from persistent follicles. Females subjected to low progesterone concentration, in the absence of a corpus luteum, have an increase in LH pulsatility, similar to the LH secretion detected during the follicular phase of the estrous cycle (Kojima et al, 1992;Roberson et al, 1989). The increased frequency of LH pulses apparently impairs the temporal relationship between oocyte and preovulatory follicle maturation (Austin et al, 1999).…”

Reduction of body-weight gain enhances in vitro embryo production in overfed superovulated dairy heifers

“…OPU 1 and 2 were performed during the luteal phase, whereas after OPU 2 and until the end of the experiment, heifers were under the effect of norgestomet implants (Fig. 1), and secretion of progesterone decreased to very low levels, as already described (Kojima et al 1992, Stegner et al 2004. Plasma progesterone remained very low for the two groups of heifers during period 2.…”

Utilização prolongada de dispositivo intravaginal contendo progesterona (CIDR®) para indução de folículos persistentes em receptoras de embrião bovino

“…Resultados semelhantes foram obtidos por Kojima et al (1992), em que a P 4 exógena não suprimiu a liberação dos pulsos de LH na mesma extensão que a P 4 endógena secretada pelo CL.…”