Abstract
The present study aimed to determine the relationship among changes in the number of primordial and primary follicles, ovarian weight and concentrations of androstenedione (A), estradiol-17 β (E2), progesterone (P4), follicle-stimulating hormone (FSH) and luteinizing hormone (LH) in the bovine fetus between day-90 and -150 of gestation. Fetal ovaries were obtained from 25 pregnant cows. Histological sections of the ovaries were examined to determine the number of preantral follicles. The hormone concentrations were determined by enzyme immunoassay. Ovarian weight increased in parallel with fetal age. No clear changes in the number of primordial follicles were observed in this period. Primary follicles were observed in ovarian sections at day-100 and the number of primary follicles increased in parallel with fetal age between day-90 and -120, and afterwards it significantly increased (p<0.05) at day-130. Around day-120, the number of primary follicles increased with the serum concentrations of A and E2. However, no relationships among number of primary follicles and concentrations of FSH and LH were observed in this period. These results indicate that the number of primary follicles markedly increases around day-130 of gestation, the increase in the number of primary follicles is associated with an increase in the concentrations of A and E2 in the fetal serum, and the growth and differentiation of primordial and primary follicles are independent of FSH and LH.
