Transvaginal ultrasound-guided oocyte retrieval (opu: Ovum pick-up) in cows and mares

For about three decades, transvaginal ultrasound-guided oocyte retrieval (OPU, ovum pick-up) has been successfully adapted from human reproductive medicine to the use in cattle and later on in the horse. Over time, it turned out to be a reliable and minimally invasive method to collect (immature) oocytes from genetically high valuable donors on a repeated basis. While a large part of the success of this procedure relies on the availability of a reliable in vitro embryo production system, a major prerequisite remains the collection of good-quality oocytes. The current chapter will focus specifically on oocyte retrieval technology. Following a detailed description of OPU equipment, the technical and biological factors affecting oocyte retrieval in living donors are discussed extensively with particular interest on the need of donor preparation by hormonal stimulation. Attention will also be given to donor health issues related to repeated oocyte retrieval. Finally, a state of the art of OPU in the mare is given describing additional physiological aspects of the equine oocyte and embryo implying additional challenges both for oocyte retrieval and in vitro embryo production.