Indução de codominância e dupla ovulação e novas abordagens em luteólise de bovinos / Induced codominance and double ovulation and new approaches on luteolysis in cattle

AUTOR(ES)
FONTE

IBICT - Instituto Brasileiro de Informação em Ciência e Tecnologia

DATA DE PUBLICAÇÃO

26/02/2010

RESUMO

The day-4 ablation model for increasing the incidence of double ovulations in heifers was used for the chapters 2 and 3. In this regard, follicles ≥ 5 mm were ablated at 4 d post-ovulation to induce a prominent FSH surge and a new follicular wave, and two injections of prostaglandin F2α (12 h apart) were given two days later (6 d) to favor ovulation. The objective of the first study (Chapter 2) was to compare follicle growth and plasma hormone concentrations associated with single versus double ovulations. From a total of 31 heifers, 16 (52%) or 15 (48%) developed, respectively, a single or more than one dominant follicle (≥ 10 mm) in the follicular wave after ablation. For heifers with two dominant follicles, second-largest follicle ovulated in 9 (60%) heifers and the overall double ovulation rate was 29% (9/31). Follicle diameters and plasma hormone concentrations were compared between single (n = 12) and double ovulators (n = 8). When the data were normalized to the peak of LH surge, a lower concentration of FSH averaged over hours and greater concentrations E2 before and at peak were observed in double ovulators. Consequently, the interval from follicle deviation to the preovulatory peak of LH surge was shorter and the diameter of the largest preovulatory follicle was smaller in double than single ovulators. In double-ovulating heifers when the peak of LH/FSH surge was observed approximately 14 h before than singleovulating, the ovulatory F1 was 1.5 mm smaller. The objective of the chapter 3 was to determine the role of the oestratiol-17β (E2) in reported follicle and hormone differences between single and double ovulations. The E2 was given to heifers for eight treatment (1.2 mg/treatment) or four treatments (0.07 or 0.09 mg/treatment) at 6-h intervals in two experiments beginning at the time off the expected deviation (n = 6 to 8 heifers/treatment group). In each experiment, the E2 treatments induced concomitant preovulatory surges in LH and FSH at mean of 24 to 34 h after first treatment, compared to 58 h in the vehicle groups. At the time of the LH peak, the diameter of the preovulatory follicle was a mean of 13 mm in the vehicle groups and 10 mm in all E2- treated groups. Thus, E2 treatments induced a significantly earlier LH surge with ovulation of significantly smaller follicles. The E2 treatment did not lower the FSH concentrations before the preovulatory FSH surge as has been reported for double ovulations. The 0.15 mg doses of E2 were associated with greater FSH concentration at peak of the preovulatory FSH surge, but the 0.07 or 0.09 mg doses did not have a similar effect. Results did not support the hypothesis that E2 is responsible for the reported reduced FSH concentrations before the preovulatory FSH surge in double ovulators. Results supported the hypotheses that increased E2 concentrations in heifers with double preovulatory follicles accounts for the reported earlier occurrence of the preovulatory LH surge and smaller preovulatory follicles in double ovulations. The luteolytic effects of exogenous prostaglandin F2alpha (PGF) were also studied during mid-diestrus in 42 Holstein heifers. Plasma concentrations of PGF were assessed by assay of PGFM. In experiment 1, a single intrauterine injection of 4.0 mg of PGF into the uterine horn ipsilateral to the corpus luteum resulted in a precipitous progesterone decline, whereas sequential injections of 0.25 or 1.0 mg every 12 h resulted in a stepwise decrease (P<0.05) following each injection. A progesterone increase occurred during the first 5 min before the luteolytic decrease but only for the 4.0-mg dose. From the results of experiment 2, a 2-h intrauterine infusion of a total of 0.5 mg of PGF was judged to best simulate a natural PGFM pulse. In experiment 3, simulation of sequential pulses at 12-h intervals resulted in a continuous precipitous decrease in progesterone to <1 ng/ml by the beginning of the fourth simulated pulse. In contrast, a single simulated pulse resulted in a 6-h progesterone decrease to a constant concentration for 3 days after treatment, followed by a return to control concentrations. Results indicated that excessive PGF doses may stimulate nonphysiologic progesterone responses and supported the hypothesis that sequential PGF pulses are required to stimulate natural luteolysis in cattle.

ASSUNTO(S)

nutricao e alimentacao animal luteólise ovulação dinâmica folicular perfil hormonal luteolysis ovulation follicular dynamics hormonal profile

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