Pattern of Ovarian Follicular Development and Steroid Hormone Concentrations during Estrous Cycle of Lohi Sheep
Muhammad Younis1, Muhammad Irfan-ur-Rehman Khan1*, Mustansar Abbas1, Ali Murtaza1, Imran Mohsin2, Muhammad Shahzad3 and Muhammad Zahid Tahir1
Follicular development of three (n = 16; A) and four-wave (n = 2; B) cycles in Lohi sheep. Diameters (mean ± SEM) of the largest (F1) and subordinate (SF) follicles were monitored daily for two consecutive ovulations via transrectal ultrasonography. The frequency of 3-wave cycles was relatively greater (p<0.05) than the 4-wave cycles i.e., 87% vs. 13%, respectively.
Changes (mean ±SEM) in diameter of corpus luteum, plasma concentrations of progesterone (P4; n= 4) and estradiol-17β (E2; n= 4). The CL became visible by Day 4, reaching a plateau on Day 9.0±0.1 and luteolysis began by Day 12.2 ± 0.2 after the ovulation. The CL diameter was directly associated with the plasma progesterone concentration during the cycle (r = 0.93; p<0.05). Multiple low peaks of plasma E2 during the luteal phase (Days 1-14) and a preovulatory peak was observed during the follicular phase (Days 14-15). Arrow indicates the ovulation.
Relationship of the largest follicle (F1) and subordinate (SF) follicle (diameter; mean±SEM) with that of plasma estradiol-17β concentration (E2) during the preovulatory period in Lohi sheep. The plasma E2 increased with the diameter of preovulatory follicles (r = 0.84; p<0.05) and reached at maximum concentration 48h before ovulation.
Representative ovarian ultrasound images of Lohi sheep. A) Ovary having a corpus luteum (CL) with cavity (CV). B) Ovary detected cranial to the urinary bladder (UB) showing a CL, dominant follicle (DF), and a subordinate follicle (SF). C) Ovary having multiple small follicles (F) at the time of follicular wave emergence (WE). D) Ovary showing mid-luteal phase CL and follicles (F).