Prepuberal Heifers as Oocyte Donors in Cattle Breeding Programs

The goal of this project is to shorten the generation interval (GI) in cattle by developing efficient methods for collection of developmentally competent oocytes from the ovaries of prepuberal heifers. The methods could then be offered as a service to our clients. Genetics gains are being limited by the length of the GI, inefficiencies in new reproductive technologies, and the low rates of selection intensity of dams in production herds. Multiple ovulation and embryo transfer (MOET) programs and transvaginal ultrasonically guided ovum pick-up (OPU) throughout the estrous cycle have been used to increase the selection intensity of dams. The variability of superovulation and low rates of development of the embryos has limited the number of offspring produced and has had little impact on the GI. Collection of oocytes from prepuberal heifers offers the best method for decreasing the GI but lack of developmental competence of the oocytes limits its use. A more complete understanding of the temporal changes occurring in the nucleus and ooplasm during oocyte growth, maturation, fertilization and early development is essential to development of this technology. The aim of the proposed studies is to develop efficient methods for collection of oocytes from the ovaries of gonadotrophin-stimulated prepuberal heifers by comparing effects of superovulatory treatments and the effect of donor age on cellular and functional changes occurring during maturation and IVMFC. The information obtained will be used as the basis for developing new and innovative methods for increasing the efficiency of superovulation and in vitro technologies applicable to bovine oocytes and embryos.