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Reproductive cycles in sheep.
Pawel M Bartlewski1, Tanya E Baby, Jennifer L Giffin
1Department of Biomedical Sciences, Ontario Veterinary College, University of Guelph, 50 Stone Road, Guelph, Ontario, Canada. pmbart@uoguelph.ca
Animal Reproduction Science
|March 18, 2011
Summary
Advances in ultrasonography reveal ovarian activity in sheep, showing follicle growth in waves controlled by follicle-stimulating hormone (FSH). Prolific breeds exhibit distinct patterns in ovulation and progesterone levels.
Area of Science:
- Reproductive Biology
- Veterinary Science
- Animal Physiology
Background:
- Real-time ultrasonography has revolutionized ovarian biology research.
- Non-invasive monitoring allows repeated assessment of ovarian structures in conscious animals.
Purpose of the Study:
- To review ovarian activity in sheep using transrectal ultrasonography.
- To correlate ovarian activity with circulating gonadotrophins and ovarian steroids during reproductive cycles.
Main Methods:
- Transrectal ultrasonography for monitoring ovarian structures.
- Measurement of circulating concentrations of gonadotrophins (e.g., FSH) and ovarian steroids (e.g., estradiol, progesterone).
Main Results:
- Follicular growth occurs in waves (3-4 per interovulatory interval), influenced by FSH.
- Estradiol secretion from dominant follicles peaks at maximum diameter.
- Prolific ewes may ovulate follicles from the last two waves, have more but smaller corpora lutea (CL), and lower progesterone levels.
Conclusions:
- Follicular wave emergence is FSH-dependent; diminished responsiveness can reduce wave numbers.
- Evidence questions strong follicular dominance in ewes, unlike cattle.
- Luteal progesterone influences antral follicular development in ewes.
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