Follicle deviation and diurnal variation in circulating hormone concentrations in mares

• Published in: Animal reproduction science 2007-07, Vol.100 (1), p.197-203
• Main Authors: Ginther, O.J., Utt, M.D., Beg, M.A.
• Format: Article
• Language: English
• Subjects: Animals; blood sampling; Circadian Rhythm - physiology; Diurnal variation; estradiol; Estradiol - blood; estrous cycle; Female; Follicle deviation; hormone metabolism; Horses - blood; Horses - physiology; Hydrocortisone - blood; luteinizing hormone; Luteinizing Hormone - blood; Mares; Ovarian Follicle - physiology; ovarian follicles; preovulatory period; progesterone; Progesterone - blood; Steroids; Testosterone - blood; Time Factors
• ISSN: 0378-4320; 1873-2232
• DOI: 10.1016/j.anireprosci.2006.08.025

The temporal relationships between follicle deviation and systemic hormone concentrations were studied in mares. Blood samples were obtained at 01:00, 07:00, 13:00, and 19:00 h from nine mares throughout an interovulatory interval. Diurnal variation in progesterone occurred on Days 4–12 and in LH on Days 4 and 5; the lowest concentration for both hormones was at 13:00 h. Ultrasonically observed deviation in the ovulatory follicular wave began on Day 15.7 ± 0.5 (ovulation = Day 0). An increase ( P < 0.002) in LH began on Day 14 before the beginning of deviation, and an increase ( P < 0.05) in estradiol began at the beginning of deviation. Testosterone concentrations began to increase ( P < 0.05) 2 days after the beginning of deviation and reached maximum 1 day before the next ovulation. The beginning of deviation was encompassed by a decline ( P < 0.003) in cortisol concentrations, and the concentrations remained low during the preovulatory period.