Origin of the preovulatory follicle in Mouflon sheep (Ovis gmelini musimon) and effect on growth of remaining follicles during the follicular phase of oestrous cycle

摘要

Daily transrectal ultrasonographies were conducted to study development of all follicles with antral diameters greater than or equal to2 mm during the follicular phase of oestrous cycle in Mouflon, a strictly monovular wild-sheep. A total of 14 follicular phases was studied after oestrus synchronization with two cloprostenol doses, 9 days apart, in five cyclic Mouflon ewes. In 13 cycles (92.8%), the ovulatory follicle arose from those antral follicles present in both ovaries when luteolysis was induced, being the largest one with a mean size of 4.4 +/-0.3 mm. at that moment in 10 cycles (76.9%). The remaining cycles had a larger follicle, but it was decreasing in size. Appearance of new follicles greater than or equal to2 mm in size remained unaffected during the follicular phase (3.7 +/- 0.2), but there was found a linear decrease in the number of those growing to > 3 rum (2.5 +/- 0.4 to 1.1 +/- 0.2, P < 0.05) and greater than or equal to4 turn (0.6 +/- 0.2 to 0.1 +/- 0.1, P < 0.005), detection of new follicles growing to greater than or equal to5 mm was negligible. Then, number of medium (4-5 mm) growing follicles present in both ovaries decreased from 1.5 +/- 0.3 at 0 h to 0.3 +/- 0.1 at 72 h (P < 0.005). In conclusion, the single ovulatory follicle is the largest growing follicle present in both ovaries at the moment of luteolysis. This follicle is selected to grow and ovulate while development of other follicles is inhibited.