Abstract
The objective of this study was to compare the follicular population during spontaneous and PGF 2α induced oestrous cycles in Nili-Ravi buffaloes. In Exp.1, (n = 13 oestrous cycles) follicular population was monitored using ultrasonography on alternate days. Buffaloes were monitored for ovarian follicles from day 0 (first oestrus) until next oestrus. These animals were observed for oestrus twice daily using a teaser bull. Of 12 oestrous cycles, 9 (75%) had two waves of follicular activity and only 3 (25%) had three waves during the oestrous cycle. The mean number of small, medium and large follicles among various days of the oestrous cycle between two and three waves of follicular development were not significantly different (p>0.05). In Exp. 2, follicular population 3 days before oestrus was compared in buffaloes undergoing spontaneous (n = 12 oestrous cycles) and PGF 2α induced (n = 6) luteolysis. The mean number of small and large follicles increased (p<0.05) and the number of medium follicles decreased (p<0.05) during the 3 days before oestrus in buffaloes undergoing induced luteolysis as compared to those with spontaneous luteolysis. These results showed that the mean number of small, medium and large follicles among various days of the oestrous cycle were similar between the two and three waves of follicular development, and three days before oestrous the number of small, medium and large follicles altered due to induced luteolysis on day 9, compared to those with spontaneous luteolysis.
Highlights
Researchers utilizing repeated ultrasonic imaging to monitor ovarian follicles in different size categories (Pierson and Ginther, 1987) or individual follicles (Sirois and Fortune, 1988) over time have confirmed the postulate by Rajakoski (1960) that follicular growth occurs in a wave-like pattern
A follicular wave is characterized by the emergence of a cohort of follicles ≥4 mm in diameter (Knopf et al, 1989), from which one large follicle develops and subordinate follicles become atretic (Ginther et al, 1989)
Two or three follicular waves occur within a single oestrous cycle (Ginther et al, 1989; Knopf et al, 1989; Ahmad et al, 1997)
Summary
Researchers utilizing repeated ultrasonic imaging to monitor ovarian follicles in different size categories (Pierson and Ginther, 1987) or individual follicles (Sirois and Fortune, 1988) over time have confirmed the postulate by Rajakoski (1960) that follicular growth occurs in a wave-like pattern. A follicular wave is characterized by the emergence of a cohort of follicles ≥4 mm in diameter (Knopf et al, 1989), from which one large follicle develops and subordinate follicles become atretic (Ginther et al, 1989). Two or three follicular waves occur within a single oestrous cycle (Ginther et al, 1989; Knopf et al, 1989; Ahmad et al, 1997)
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