DOI: 10.1051/rnd:2001142

Reprod. Nutr. Dev. 41 (2001) 427-437

Factors influencing oocyte and embryo quality in cattle

Patrick Lonergan, Dimitrios Rizos, Fabian Ward and Maurice P. Boland

Department of Animal Science / Production and Conway Institute for Biomedical and Biomolecular Research, University College Dublin, Lyons Research Farm, Newcastle, County Dublin, Ireland

(Received 15 October 2001; accepted 5 November 2001)

Abstract
Following in vitro maturation, approximately 90% of immature bovine oocytes will reach metaphase II and extrude the first polar body; approximately 80% will undergo fertilization and cleave, at least once, to the two-cell stage. However, only about 30-40% will ever reach the blastocyst stage. This would suggest that the post-fertilization part of the process of in vitro embryo production, the longest part, is the main period determining blastocyst yield. The experiments described in this paper clearly demonstrate that this is, in fact, not the case and that it is events further back along the developmental axis that determine the proportion of immature oocytes reaching the blastocyst stage. The results also show, however, that the post-fertilization culture period is of profound importance in determining the equality of those blastocysts that do develop, with those produced in vitro consistently being of inferior quality to their in vivo produced conterparts. The challenge for the future is to modify our conditions of post-fertilization embryo culture in an attempt to mimic those that occur naturally in vivo and in that way improve blastocyst quality.

Key words: Cattle / oocyte competence / embryo quality / cryopreservation

Correspondence and reprints: Patrick Lonergan
    e-mail: lonergan@pop3.ucd.ie

© INRA, EDP Sciences 2001