Role of atresia in establishing the follicular hierarchy in the ovary of the domestic hen (Gallus domesticus)

Publisher Website
Google Scholar
Abstract
At peak laying periods the ovary of the domestic hen contained 30-100 small yolky follicles with diameters varying between 1 and 8 mm. The number of these healthy follicles decreased with increasing size in that there were about 20 follicles with a diameter of 1-2 mm and 1 follicle (mean < 1) with a diameter of 7-8 mm. The number of follicles with diameters > 8 mm (the hierarchy of large, yolky follicles) varied between 4 and 7. By using a dye-marker, growth from 3 to 5 mm was estimated to take 3 days; from 5 to 8 mm; 2 days and from 8 mm to ovulation, 6 days. No information was obtained for growth between 1 and 3 mm because the dye did not enter these smaller follicles. Between 5 and 25 small yolky follicles were atretic. The reduction in the number of follicles with time and the high incidence of atresia suggest that this is a normal fate of small yolky follicles in birds with a high rate of lay. In marked contrast, only 1 large yolky follicle was observed to be atretic throughout the whole experiment. These 2 very different levels of atresia serve to define 2 distinct groups of follicles in the size range studied. Ovulation rate appears to be the product of 2 complementary mechanisms, one for the initiation of growth and the other controlling the rate at which the small yolky follicles are lost through atresia.