<b>Potential of growth factors and steroid hormones from cell cultures to improve <i>in vitro</i> fertilization in bovine</b><b></b>

The application of biotechnology attempts to improve the efficiency of animal reproduction, specifically to produce cattle of high quality and quantity. One successful and efficient method in the field of reproduction is embryo transfer. The capacity of donor females to produce embryos limits the number of embryos that can be produced <i>in vivo</i>. In this instance, an alternate source of embryos is <i>in vitro</i> embryo production. Two mitogenic chemicals, estrogen and insulin-like growth factor-I (IGF-I), can be employed to promote and accelerate cell proliferation. The liver and other tissues release the polypeptide growth factor IGF-I, also known as somatomedin, in response to growth hormone stimulation. The molecular weight of the 70 amino acids that make up IGF-I is 7649 Da or 7.65 kDa. Estrogen, specifically estradiol, is a steroid hormone produced by developing follicles in the ovary, corpora lutea, and placenta. IGF-I and estrogen promote mitogenic activity in proliferating cells in paracrine, autocrine, and endocrine ways. IGF-I and estrogen can be produced by the liver and ovaries. Both the ovary and the liver are the primary producers of the sex steroid estrogen and IGF-I, respectively, and both may be produced using monolayer cell culture by supplementing them with either bovine serum albumin or fetal calf serum as precursor substances. IGF-I and the steroid sex hormones progesterone and estrogen in liver and cumulus cell monolayer culture may be used as a culture medium for embryo development.