Ovarian Development in Fetal and Prepubertal Pigs

Ovaries were collected from Dutch Landrace crossbred pigs ranging in age from 49 days postcoitum to 90 days after birth to quantify ovarian follicular development. Morphological changes in the ovary of the fetal and prepubertal pig indicated that egg nests were the earliest recognizable gamete cells. Primordial follicles were first observed in ovaries 68 days postcoitum, primary follicles about 75 days postcoitum and secondary follicles near the time of birth. Only a few tertiary follicles were present in ovaries from pigs 62–90 days after birth. Egg nests were the major gamete cell, accounting for 60–100% of the total from 50–68 days postcoitum. Starting 70 days postcoitum until 90 days after birth, primordial follicles accounted for about 80% of the total follicular population. There were no changes in the activity of 3β-hydroxysteroid dehydrogenase or 17β-hydroxysteroid dehydrogenase observed in ovaries from 49 days postcoitum to 90 days after birth. It appeared that ovarian follicular development continued in a linear manner unchanged by a perinatal surge in peripheral LH. Treatment with exogenous gonadotropins did not cause any recognizable change in ovaries from 5-week-old pigs. However, 2 of 4 pigs treated at 9 weeks of age had 12 ovulations each.