Circannual changes in progesterone secretion in intact ewes, luteinizing hormone secretion in ovariectomized estradiol-implanted ewes, and prolactin secretion in three sheep breeds anticipated to differ in seasonality of reproduction

• Published in: Animal reproduction science 2013-05, Vol.138 (3-4), p.194-202
• Main Authors: Goff, Katherine J, Knight, James W, Pelzer, Kevin D, Akers, R. Michael, Notter, David R
• Format: Article
• Language: English
• Subjects: anestrus; Anestrus - drug effects; Anestrus - physiology; Animals; blood; breed differences; breeding; breeding season; Breeds; Drug Implants; Estradiol - administration & dosage; Ewes; Female; Fertility - drug effects; Fertility - physiology; hormone secretion; landraces; luteinization; Luteinizing hormone; Luteinizing Hormone - blood; Luteinizing Hormone - secretion; ovariectomy; Ovariectomy - veterinary; Progesterone; Progesterone - blood; Progesterone - secretion; Prolactin; Prolactin - blood; Prolactin - secretion; Rambouillet; rams; Reproduction - drug effects; Reproduction - physiology; Seasonal breeding; Seasons; Sheep, Domestic - blood; Sheep, Domestic - metabolism; Sheep, Domestic - physiology; Species Specificity; spring; summer; Time Factors
• ISSN: 0378-4320; 1873-2232
• DOI: 10.1016/j.anireprosci.2013.03.004

Changes in progesterone secretion in intact ewes (7 or 9 per breed) and luteinizing hormone secretion in ovariectomized, estradiol-implanted ewes (9 or 10 per breed) were monitored for 12 mo in Suffolk, tropically adapted St. Croix, and OOS ewes. The OOS line is a composite population of 50% Dorset, 25% Rambouillet, and 25% Finnish Landrace breeding that was selected for 10 yr for ability to lamb in October and early November. Ewes were isolated from rams, and blood samples were collected twice weekly. Circulating prolactin concentrations were also determined from blood samples collected near the summer and winter solstice and vernal and autumnal equinox. Intact OOS ewes entered anestrus later, began the subsequent breeding season sooner, and had a shorter seasonal anestrus than Suffolk and St. Croix ewes (P ≤ 0.005). St. Croix ewes did not differ from Suffolk ewes in date of onset or cessation of breeding or duration of anestrus (P ≥ 0.06). Breed differences in duration of luteinizing hormone inhibition in ovariectomized ewes were essentially identical to those observed for duration of anestrous. Prolactin concentrations varied during the year: annual changes were larger in relatively seasonal Suffolk ewes than in tropically-derived St. Croix ewes (P