Reducing the interval between generations would significantly advance the efficiency of genetic selection, which is mainly important in species characterized by late puberty, long pregnancy and single offspring. Oocytes for in vitro embryo production can be obtained from calves, lambs, goats, foals and gilts well before puberty, either after slaughter or by less invasive methods, such as laparoscopy and transvaginal aspiration under ultrasonograph guidance. The latter two can be applied to females without greatly affecting their health and are therefore the preferred methods when animals are to be retained for breeding purposes. However, the use of transvaginal aspiration is limited to larger animals, such as 6-month old calves. The quality of oocytes from prepubertal females seems to be lower than that of adults. Although hormone stimulation of the animals and the use of enriched media improve embryonic competence of prepubertal oocytes following in vitro maturation and fertilisation, the efficiency of embryo production remains low. The is probably due to the immaturity of their cytoplasm.
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