Follicular development in the cow: hormonal regulations involved in the control of estrous cycle and post-partum period.

Described in this paper are the hormonal mechanisms involved in the follicu lar development in cows during both cycle and post-partum period. it follow s the overview of the morphological and kinetics features of follicular gro wth in cows (Hanzen et al., 2000). 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 seem s to be gonadotrop independent and is placed under control of intra-ovarian factors. The second step is dependent on the gonadotropins (Follicle Stimu lating Hormone/Luteinizing Hormone) and on intra/extra-ovarian factors, exp laining 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 est radiol and inhibin are implied in the establishment of the physiological an d morphological dominance of the follicle while the others follicles underg o atresia. This terminal follicular growth proceeds of waves which complete mechanism of regulation still remain to explore. It appears however that t he number of waves is related to both quantitative and qualitative variatio ns of progesterone along estrous cycle. The postpartum follicular growth is a complex phenomenon. its reappearance is dependent on various factors with the energetic status of the female rem aining probably the more important. Others such as suckling, progesterone i nhibition of hypothatamo-hypophysial axis during pregnancy, estradiol secre tion around parturition and finally dystocial calving are involved in the d elayed manifestation of estrous cycle by the female. Even if some factors remain to explain, a significant progress in the knowl edge of these mechanisms was more recently performed by the study of brain peptides (opioids) and respective intervention of insulin and leptin...