Recent studies on in vivo fertilisation of in vitro matured horse oocytes

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Abstract
Summary: Fresh horse oocytes dissected from slaughterhouse ovaries were allocated to two groups depending on the degree of development of the cumulus investment. In Group I, the cumulus was fully compact whereas in Group II it was partially expanded. Basic culture medium (M199) was supplemented either with 20 per cent late oestrus mare serum (M199a) or 10 per cent foetal calf serum plus gonadotrophins (M199b). At the start of the culture, 70 per cent of Group I and 28 per cent of Group II oocytes were at germinal vesicle, or germinal vesicle breakdown stages. During culture in M 199a, the proportion of oocytes reaching metaphase of second meiosis (M II) was at a maximum after 30 h in culture for Group I oocytes (61 per cent) and after 24 h in culture for Group II oocytes (68 per cent). After culture in M199b, a higher proportion of Group I oocytes (89 per cent) displayed full expansion and mucification of the cumulus than when cultured in M199a (13 per cent), although the same proportion reached M II in each medium (63 per cent and 64 per cent respectively). Fluorographs of 1‐dimensional gels of oocyte protein showed an accumulation of a polypeptide (MW 34 kDa) during culture. A total of 29 in vitro matured oocytes were transferred to the oviducts of four recently mated recipient mares judged to be at the point of ovulation. Uterine flushing of these mares eight days after surgery resulted in the recovery of seven blastocysts, two of which were then transferred surgically to the uteri of synchronised recipient mares and one pregnancy resulted.