title: Bypassing the effect of zona pellucida changes on embryo formation following cryopreservation of bovine oocytes.
abstract: OBJECTIVE
  To evaluate the effects of zona pellucida changes following the cryopreservation of bovine oocytes using two different techniques.
  
  
  METHODS
  Prospective randomised study.
  
  
  METHODS
  University research facility and IVF research laboratory, NURTURE, University of Nottingham, UK.
  
  
  METHODS
  508 bovine oocytes were collected from abattoir-derived ovaries and cryopreserved by slow freezing using standard straws and a new vitrification method using our self-constructed cryoloops. After thawing, the oocytes were inseminated by ICSI and standard IVF.
  
  
  METHODS
  Oocyte degeneration and oocyte cleavage.
  
  
  RESULTS
  Cleavage rates after IVF in fresh oocytes was higher (49.5%) than the cryopreservation groups (slow freezing: 15.4% and vitrification: 25.8%), whereas after ICSI, the rates were similar (fresh: 17.3%, slow freezing: 9.4%, vitrification: 16.0%).
  
  
  CONCLUSIONS
  Zona pellucida changes after oocyte cryopreservation significantly reduce the embryo formation rates after IVF. ICSI bypasses this complication and in selected species it could be an appropriate method of insemination.
authors.affiliation: School of Human Development, University of Nottingham, Queen's Medical Centre, Nottingham NG72UH, UK. andreas@mavrides.com
authors.forename: Andreas
authors.initials: A
authors.lastname: Mavrides
authors.forename: David
authors.initials: D
authors.lastname: Morroll
mesh_terms: D000818:Animals; D002417:Cattle; D002970:Cleavage Stage, Ovum; D015925:Cryopreservation / Q000379:methods*; D005260:Female; D005307:Fertilization in Vitro; D009865:Oocytes / Q000502:physiology*; D011446:Prospective Studies; D020554:Sperm Injections, Intracytoplasmic; D015044:Zona Pellucida / Q000502:physiology*