Plasma gonadotropin and progesterone concentrations during the estrous cycle of Finn, Suffolk and Targhee ewes

Hormonal profiles during the estrous cycle of Finn, Suffolk and Targhee ewes were compared in six ewes of each breed. Blood samples were drawn by venipuncture at 8-h intervals from onset to onset of consecutive estrous periods. Number of corpora lutea (CL) and ovarian follicles >/=3 mm in diameter on Day 10 (estrus = Day 0) were observed using endoscopy. Estrous cycle length was 14.9, 15.6 and 16.4 d (P<0.01) in Finn, Suffolk and Targhee ewes, respectively. Finns had more (P<0.001) CL (3.5) than Suffolks (2.0) and Targhees (1.8), but luteal phase progesterone concentrations were similar among breeds in peak level and area under the curve. In Finn ewes, the amplitude of the preovulatory LH surge was lower (P<0.01) and tended to occur later in estrus; otherwise LH levels and patterns were similar among breeds. A coincident follicle stimulating hormone (FSH) preovulatory surge occurred in most ewes, the amplitude of which was related to that of luteinizing hormone (LH); r = 0.67, P<0.01. Plasma FSH levels and patterns were similar in Finn, Suffolk and Targhee ewes and most ewes had three to four secretory episodes. Follicles >/=3 mm averaged 1.8, 1.0 and 1.2 (P>0.1) in Finn, Suffolk and Targhee ewes, respectively. Results indicate that the higher ovulation rate of the Finn ewe is not elicited by increased FSH levels at any stage of the estrous cycle.