Roles of biotin in growing ovarian follicles and embryonic development in domestic fowl.

It is well known that biotin deficiency causes morphological anomalies in hatchlings of fowl. An abundance of biotin in the yolk, therefore, is greatly required for maintaining reproductive functions. Although there is growing evidence for the molecular significance of the vitamin in the processes of the reproductive system in mammals, little is known about its use and roles in fowl's yolk. This review focuses on studies on the roles of biotin in the ovarian follicles and embryos of domestic fowl. Recent studies from our laboratory showed an analysis of the mechanism of biotin supply from the maternal body to follicles, or the yolk using the eggs of domestic fowl. In growing ovarian follicles, biotin was incorporated into the follicles, particularly in a large amount immediately before ovulation. Biotin incorporated from the early stage to the growth stage of ovarian follicles was stored in the protein-binding form and became free biotin again immediately before ovulation. This may be because the biotin necessary for the maintenance of embryonic growth and development should be used immediately after fertilization. In embryos, free biotin in the yolk increased shortly after fertilization. A large amount of free biotin was incorporated into the embryo at the age of 3-4 d. Biotin supply to the embryo differed among embryonic growth stages and organs, suggesting involvement in the formation of each tissue and organ. Thus, a large amount of biotin was utilized for embryonic growth, suggesting its important role in normal embryonic growth. These findings show that biotin is an essential nutrient and may play a major role in the normal morphogenesis of embryos in domestic fowl.