Ovarian follicular dynamics during the oestrous cycle in cows
1990
Putro, P.P. | Williamsom, E.P. (Murdoch Univ. Murdoch (Australia). School of Veterinary Studies) | Sawyer, J.G.
Pattern of growth and regression of ovarian follicles during oestrous cycles in eighteen Holstein cows was studied by daily transrectal ultrasonographic examinations. Follicles = 5 mm were measured and their relative locations within the ovary were determined, to follow the sequential development of each individual follicle. The daily plasma concentration of progesterone of the cows was simutaneously assessed to identify different phases of the oestrous cycle. Most oestrous cycles (13/18-72.2 %) were characterized by the growth of 3 successive dominant follicles that occure in waves. The first dominant follicle (non-ovulatory) was identified on Day 0 (day of ovulation), reached its maximum diameter on Day 8 and was detectable, on average, until Day 17 of the oestrous cycle. The second dominant follicle (non-ovulatory) was generally present between Days 5 and 20 of the oestrous cycle and reached its maximum diameter on Day 14. The third dominant follicle (ovulatory) was first detected on Day 11 of the cycle, stayed relatively stable in diameter between Days 11 and 13 then showed increased growth rate and reached its maximum diameter on Day 21, before ovulating. Some oestrous cycles (5/18=27.8 %) were characterized by the growth of only 2 dominant follicles.
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