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.
Daily transrectal ultrasonographies were conducted to study development of all follicles with antral diameters > or = 2mm 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+/- 0.3mm 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 > or =2mm 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 > or =3mm (2.5+/- 0.4 to 1.1+/- 0.2, P < 0.05) and > or = 4mm (0.6+/- 0.2 to 0.1+/- 0.1, P < 0.005), detection of new follicles growing to > or = 5mm was negligible. Then, number of medium (4-5mm) 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.
Departamento de Reproduccion Animal, SGIT-INIA, Avda. Puerta de Hierro s/n., 28040, Madrid, Spain. bulnes@inia.es
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A
Gonzalez-Bulnes
J
J
Santiago-Moreno
R M
RM
Garcia-Garcia
A
A
del Campo
A
A
Gómez-Brunet
A
A
Lopez-Sebastian
D000818:Animals; D004971:Estrus; D005260:Female; D005498:Follicular Phase; D006080:Ovarian Follicle / Q000033:anatomy & histology / Q000502:physiology*; D012756:Sheep / Q000502:physiology*