Sensitivity of follicles from prepubertal calves ovaires to in vitro stimulation with LH and FSH

Ovaries from prepubertal calves were harvested in an abattoir and quickly brought to the laboratory for the dissection of the follicles. The intact entire follicles were put in individual chambers and continuously perifused with TCM199 at the rate of 1ml/30 min. The medium was added LH at the time 60–90 min and FSH at the time 120–180 min. The perifusion lasted 5 hours and the perifused medium was collected every 30 min. The samples were assayed for Progesterone, D4-Androstenedione and Estradiol. Four different stimulations were assayed: LH +FSHc (FSH commercial with an estimated 20% LH contamination), LH + FSHp (pure FSH, with 0% LH activity), FSHc alone, and FSHp alone. No difference were observed between the treatments; this confirms the results of De Roover eet al. (this workshop) that the absence of LH is not the reason for the lack of Estradiol peak after FSH stimulation of calves ovaries in vivo. Only large follicles (diameter ³ 13 mm) were able to produce Estradiol in vitro. According to the follicular size, no difference can be measured in D4 production, but medium sized follicles produced significantly more Progesterone than small or large ones. It can be interpreted as a growing ability to produce Progesterone and the late acquisition of ability to produce Estradiol. The observation of the small proportion of follicles with diameter ³ 13 mm may be the explanation of the lack of E2 peak production after in vivo stimulation. High levels of Estradiol are suspected to be necessary for the acquisition of the oocyte competency to develop into viable embryos. The incapability of most of the follicles present in ovaries of prepubertal calves to produce significant level of E2 might be the reason of the poor results in embryo development after ovum pick-up in this kind of animal.