Comparative study on the potential reproductive differences of ewe lambs with diverse antral follicle count at an early prepubertal age

Numerous studies link the antral follicle count (AFC) and anti-Müllerian hormone (AMH) levels with the ovarian reserve and a wide variety of fertility indices in adult animals and women. In adulthood both parameters seem to remain relatively constant for each individual during long periods of time but show a high variability between individuals. However, little is known about differences in AFC and AMH during the prepubertal period and their eventual implication on ovarian function or future reproductive life. Thus, this dissertation aimed to determine differences in the early prepubertal period, in the evolution from the prepubertal period to adulthood and in adulthood between ewe lambs classified by their AFC at an early prepubertal age. In the early prepubertal period animals with a low AFC showed, although not accompanied by a reduction in the size of the primordial follicle pool, a lower response to gonadotrophin stimulation, poor oocyte in vitro developmental competence and delayed increase in AMH levels. Differences in the AFC and in the response to ovarian stimulation tent to disappear with age. In adulthood we could not find differences in the response to a multiple ovulation and embryo transfer treatment or in the oestrus cycle. However, ewe lambs with higher AFC and AMH in the early prepubertal age still had higher pregnancy rates at first breeding season. Hence, AFC and AMH might represent an interesting tool for ewe selection at an early age.