Distribution of ovarian follicular populations in the dairy cow within 35 days after parturition

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Abstract
Ovaries were obtained at slaughter from 12 Holstein dairy cows at 15, 25 or 35 days after their 4th calving. Non-atretic and atretic antral follicles were separated into 6 size classes according to size and the numbers in each class were expressed as a percentage of the total for each ovary. Non-atretic follicles of diameter 0.16-0.28 mm decreased from 27.5% at day 15 to 1.5% at day 35 those of 0.29-0.67 mm and 0.68-1.57 mm diameter increased from 37.4 to 47.2% and from 11.5 to 17.3%, respectively, (all P < 0.05). The proportions of follicles measuring 1.58-3.698, 3.69-8.56 and > 8.56 mm remained almost constant. The atretic follicles of 0.29-3.68 mm varied significantly in number according to the post-partum interval and to whether they were in the ovary containing the CL [corpus luteum] of pregnancy. The CL of pregnancy and/or the conceptus have a carry-over effect on the rate of growth of the antral follicles even after parturition.