Follicular development in the cow : hormonal regulations involved in the control of oestrous cycle and post-partum period | Le developpement folliculaire chez la vache. Mecanismes hormonaux au cours du cycle et du post-partum

The hormonal mechanisms involved in the follicular development in cows during both cycle and post-partum period are described. It follows the overview of the morphological and kinetics features of follicular growth in cows. In this species, the follicular growth is composed of two steps: the first one concerns the follicles reaching a maximal size of 5 mm. This stage seems to be gonadotrop independent and is placed under control of intra-ovarian factors. The second step is dependent on the gonadotropins (Follicle Stimulating Hormone/Luteinizing Hormone) and on intra/extra-ovarian factors, explaining the follicular recruitment, selection and dominance. The follicular recruitment is mainly dependent of the Follicle Stimulating Hormone as well as the somatotropin and some of the growth factors. The increase in estradiol secretion at the beginning of the "selection" is related to the increase in Luteinizing Hormone pulses. Afterwards, both estradiol and inhibin are implied in the establishment of the physiological and morphological dominance of the follicle while the others follicles undergo atresia. This terminal follicular growth proceeds of waves which complete mechanism of regulation still remain to be explore. It appears however that the number of waves is related to both quantitative and qualitative variations of progesterone along oestrous cycle. The postpartum follicular growth is a complex phenomenon. Its reappearance depend on various factors with the energetic status of the female remaining probably the more important. Others such as suckling, progesterone inhibition of hypothalamo-hypophysial axis during pregnancy, estradiol secretion around parturition and finally dystocial calving are involved in the delayed manifestation of estrous cycle by the female. Even if some factors remain to be explain, a significant progress in the knowledge of these mechanisms was more recently performed by the study of brain peptides (opioTds) and respective intervention of insulin and leptin.