Article

Reproductive cycles in sheep.

Department of Biomedical Sciences, Ontario Veterinary College, University of Guelph, 50 Stone Road, Guelph, Ontario, Canada.
Animal reproduction science (Impact Factor: 1.56). 02/2011; 124(3-4):259-68. DOI: 10.1016/j.anireprosci.2011.02.024
Source: PubMed

ABSTRACT During the last three decades, there has been remarkable progress in many aspects of ovarian biology due to advances in real-time ultrasonography, which permits non-invasive, repeated monitoring of ovarian structures in conscious and non-anaesthetised animals. This review is primarily concerned with ovarian activity, as determined by transrectal ultrasonography, and measurements of circulating concentrations of gonadotrophins and ovarian steroids during reproductive cycles in sheep. The growth of antral follicles reaching ostensibly ovulatory sizes occurs in a wave-like pattern throughout the breeding season in both prolific and non-prolific breeds of sheep. There are typically 3 or 4 waves of follicle development during the interovulatory interval. Follicular wave emergence is primarily controlled by changes in circulating concentrations of follicle-stimulating hormone (FSH) but diminished ovarian responsiveness to gonadotrophic signals may result in reduced numbers of follicular waves. In cyclic ewes, the largest ovarian follicles acquire the ability to secrete oestradiol from the day of emergence with peak oestradiol secretion occurring about the time they reach maximum diameter. The high ovulation rate in some prolific breeds may be achieved by the ovulation of follicles from the last two waves of the interovulatory interval. Prolific ewes tend to produce more but smaller corpora lutea (CL) and have lower serum concentrations of progesterone during the luteal phase of the oestrous cycle as compared to less prolific genotypes. Lastly, recent studies of the endocrine influences on ovarian function have brought into question the existence of strong follicular dominance, as seen in cattle, and provided new insights into the effects of luteal progesterone on antral follicular development in ewes.

1 Bookmark
 · 
198 Views
  • [Show abstract] [Hide abstract]
    ABSTRACT: The mRNA expression and localization of Aquaporin 3 (AQP3) were investigated in the ovarian follicles of ewes at different stages of development (primordial, primary, secondary, small, and large antral). The gene expression was quantified by qPCR, while the protein identification and localization were determined by Western blot and immunohistochemistry, respectively. Analysis revealed that AQP3 mRNA was detected only in the antral follicles, whereas the protein expression was detected in the oocyte and granulosa cells in all stages of follicular development. The latter observation suggests that the presence of AQP3 in follicles of all categories, especially in the antral follicles, provides novel insights on the mechanisms that regulate the flow of water between cells during the formation of antral follicles in sheep.
    Acta histochemica 01/2014; · 1.61 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Developmental exposure to BPA adversely affects reproductive function. In sheep, prenatal BPA treatment induces reproductive neuroendocrine defects, manifested as LH excess and dampened LH surge and perturbs early ovarian gene expression. In this study we hypothesized that prenatal BPA treatment will also disrupt ovarian follicular dynamics. Pregnant sheep were treated from days 30 to 90 of gestation with 3 different BPA doses (0.05, 0.5, or 5mg/kg BW/day). All female offspring were estrus synchronized and transrectal ultrasonography was performed daily for 22days to monitor ovarian follicular and corpora lutea dynamics. Blood samples were collected to assess hormonal preovulatory changes and luteal progesterone dynamics. Statistical analysis revealed that the time interval between the estradiol rise and the preovulatory LH surge was shortened in the BPA-treated females. None of the three BPA doses had an effect on corpora lutea, progestogenic cycles, and mean or duration of ovulatory and non-ovulatory follicles. However, differences in follicular count trajectories were evident in all three follicular size classes (2-3mm, 4-5mm, and≥6mm) of prenatal BPA-treated animals compared to controls. Number of follicular waves tended also to be more variable in the prenatal BPA-treated groups ranging from 2 to 5 follicular waves per cycle, while this was restricted to 3 to 4 waves in control females. These changes in ovarian follicular dynamics coupled with defects in time interval between estradiol rise and preovulatory LH release are likely to lead to subfertility in prenatal BPA-treated females.
    Toxicology and Applied Pharmacology 06/2014; · 3.98 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: This study assessed the effect of melatonin deprival on ovarian status and function in sheep. Experimental procedures were carried out within two consecutive breeding seasons. Animals were divided into two groups: pinealectomized (n=6); sham-operated (n=6). The completeness of the pineal gland removal was confirmed by the plasma concentration of melatonin. Ovarian status was monitored by ovarian ultrasonography during one year to study reproductive seasonality. Follicles and corpora lutea growth dynamics were assessed during an induced oestrous cycle. Since melatonin effects on the ovary may be also mediated by its antioxidant properties, plasma trolox equivalent antioxidant capacity (TEAC) was determined monthly during one year. Pinealectomy significantly extended the breeding season (310 ± 24.7 vs 217.5 ± 24.7 days in controls; p<0.05). Both pinealectomized and sham-operated ewes showed a well-defined wave-like pattern of follicle dynamics; however, melatonin deficiency caused fewer waves during the oestrous cycle (4.3 ± 0.2 vs. 5.2 ± 0.2; p<0.05) because waves were one day longer when compared with the controls (7.2 ± 0.3 vs. 6.1 ± 0.3; p<0.05). The mean area of the corpora lutea (105.4 ± 5.9 vs. 65.4 ± 5.9 mm2; p<0.05) and progesterone plasma levels (7.1 ± 0.7 vs 4.9 ± 0.6 ng/mL; p<0.05) were significantly higher in sham-operated compared with pinealectomized ewes. In addition, TEAC values were significantly lower in pinealectomized ewes compared to control ones. These data suggest that melatonin, besides exerting its well-known role in the synchronization of seasonal reproductive fluctuations, also influences the growth pattern of the follicles and the steroidogenic capacity of the corpus luteum.
    Reproduction 02/2014; · 3.56 Impact Factor

Full-text

Download
74 Downloads
Available from
May 21, 2014