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Seasonal variations in the developmental competence of bovine oocytes matured in vitro
  1. C. C. Silva, BSc, PhD1,
  2. H. J. D. Rosa, BSc, PhD1 and
  3. P. G. Knight, BSc, MSc, PhD1
  1. 1School of Animal and Microbial Sciences, University of Reading, Whiteknights, Reading RG6 6AJ


Ovaries were collected over a period of two years from heifers slaughtered at under 30 months of age and used to harvest 1757 oocytes. After in vitro maturation, fertilisation and culture, the proportions of oocytes and cleaved embryos that developed to blastocysts were significantly higher (P<0·01) in the autumn, from September to November, than in the spring, from March to May. In contrast, embryo development, as assessed by oocytes that developed to eight or more cells and blastocysts, was lowest (P<0·01) in the spring. These results were consistent during the two-year study, indicating a seasonal fluctuation in oocyte competence.

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  • Dr Silva’s present address in Departamento de Ciências Agrárias, CITA-A, Universidade dos Açores, 9701 851 Terra Cha, Portugal

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