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Distribution of follicular growth, atresia and ovulation in the ovary of the domestic hen (Gallus domesticus) at different ages

Summary. Ovaries of laying hens of 14, 18, 30, 45 and 86 weeks of age were divided transversely into two or more distinct regions. Differences in follicular populations between these regions were observed. The central segments of the ovary in birds of 14 weeks of age produced most of the visible (> 0·5 mg) developing follicles (P < 0·01). This was a transient effect during ovarian maturation. In birds of 18 weeks of age, but not yet in lay, more follicles of > 8 mm in diameter were observed in the anterior part of the ovary than the posterior part (P < 0·05). Follicles of this size are almost certain to ovulate. The posterior segment of the ovary of birds of 30, 45 and 86 weeks of age contained more follicles beginning the rapid growth phase, as measured by follicles of 1·4–1·8 mm in diameter, than did the anterior segment (P < 0·01). Higher levels of atresia in the posterior segment (P < 0·001) resulted in fewer follicles of > 8 mm (P < 0·001) and fewer post-ovulatory follicles than in the anterior segment. We conclude that most of the eggs produced during the hen's laying year must be from ovulations from the anterior part of the ovary.

Keywords: hen; age; ovary; follicular population distribution; ovulation