LAUSR

Pakistan has 30.9 million heads of sheep; however, little information is available on their reproductive aspects. The objective of this study was to document ovarian physiology and endocrinology of Lohi ewes during the oestrous cycle. Nine Lohi ewes, synchronized by administering single prostaglandin F2α (PGF2a; Cyclomate, Star Laboratories), were monitored for ovarian follicular dynamics using transrectal ultrasonography (7.5 MHz, HS-1500, Honda) for two consecutive oestrous cycles during the breeding season (September to November 2018). Changes in plasma progesterone and oestradiol-17β concentrations of ewes (n = 9) were also determined during the oestrous cycle using radioimmunoassay. The interovulatory interval of Lohi ewes averaged 17.0 ± 0.1 days, and the duration of follicular and luteal phases was 4.6 ± 0.2 and 11.3 ± 0.2 days, respectively. Follicles emerged in either 3- or 4-wave patterns, but the frequency of the 3-wave pattern was higher than that of the 4-wave (87 vs. 13%, respectively; P = 0.05). Following ovulation (Day 0), follicles (=3 mm) in 3-wave cycles (n = 14) emerged on Days 0.7, 5.2, and 10.5, whereas in 4-wave cycles (n = 2) follicles emerged on Days 0.1, 4, 8.5, and 11.5. The maximum diameter of preovulatory follicles and corpora lutea (CL) were 5.4 ± 0.3 and 10.4 ± 0.3 mm, respectively. Regardless of the wave pattern, single ovulation occurred in each cycle. The CL was first detectable on Day 4 ± 0.1, it reached maximum diameter on Day 9 ± 0.1, and luteolysis began on Day 12.2 ± 0.2 of the cycle. The peak plasma oestradiol-17β concentration (42.5 ± 2.6 pg mL−1) was observed 48 h before ovulation and correlated with the diameter of the preovulatory follicle during the follicular phase (r = 0.84; P < 0.05). The peak plasma progesterone concentration (11.8 ± 1.7 ng mL−1) was observed on Day 9 ± 0.1 and coincided with the diameter of CL throughout the oestrous cycle (r = 0.93; P < 0.05). In conclusion, the majority of oestrous cycles in Lohi ewes had a 3-wave pattern and were mono-ovulatory in nature.