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Puncture of immature ovarian follicles in bovine assisted reproduction.

Transvaginal, ultrasound-guided follicular aspiration (OPU) is the method of choice to retrieve immature oocytes from highly valuable living donor cows for in vitro embryo production. In the introduction, we comment on general techniques of oocyte retrieval. In the second part, we describe the OPU technique from a technical point of view, and we discuss the factors that influence the quality and quantity of the oocytes retrieved. Firstly, there is a group of technical factors such as aspiration procedure, needle type, and the influence of the aspiration vacuum on cumulus oocyte complex morphology. Secondly, there is a huge group of biological influences, e.g. hormonal stimulation prior to follicle puncture, timing of the procedure relative to the estrous cycle, age, breed, and physiological condition of the donor. Subsequently, the use of OPU in combination with in vitro embryo production for the treatment of bovine sterility patients is discussed, as a way to obtain additional offspring from donors with impaired fertility. Reports on donor animal health and reproductive performance following repeated OPU are commented upon. Finally, future research possibilities related to the OPU technique are discussed. Additional gain is expected from the development of better ultrasound equipment, permitting optimal visualization of the smallest follicles. In addition, OPU equipment will be used for related purposes, such as repeated retrieval of ovarian biopsies, and the injection of local ovarian mediators, which will permit to study local paracrine hormonal effects, and their influence on oocyte quality.