Identification at the onset of luteolysis of follicles capable of ovulation in the ewe

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Abstract
Follicles of various sizes at the surface of the ovary were ablated by electrocautery at the time of cloprostenol-induced luteolysis in ewes and the interval from cloprostenol treatment to the onset of the LH [luteinizing hormone] surge determined as an index of the time from luteolysis to ovulation. When follicles 2-4 or > 4 mm diameter remained in the ovaries, the interval from cloprostenol treatment to the onset of the LH surge was similar to that in sham-operated (control) ewes (55-60 h), whereas when the only follicles remaining were < 2 mm, the interval was extended by 24 h (P < 0.05). Follicles capable of ovulating evidently can be selected from those .gtoreq. 2 mm diameter at luteolysis, emphasizing the flexibility of the sheep ovary in its final selection of the ovulatory follicle.