The pattern of follicular growth and atresia in the ovine ovary.

The ovaries of 21 2-year-old Merino ewes at various stages of the oestrous cycle were serially sectioned and all follicles > 0·5 mm in diameter were counted and measured. The mean number of normal follicles > 0·5 mm in diameter was 19· 9 per ewe, of which 8·7 were > 1 mm in diameter. The mean numbers of follicles > 0·5 mm in diameter in 'early', 'advanced' and 'late' stages of atresia were 4· 6, 9· 0 and 12· 3 respectively. Early atresia was rarely seen in follicles < 1 mm in diameter; the greatest incidence was in follicles of diameter 1· 5-2' 5 mm.

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