Received February 15, 2005
Accepted March 29, 2005

Aims of the study: To assess the effect of different tissue sizes on the morphology of primordial and primary follicles after cryopreservation. Design: Laboratorial controlled experiment. Comparative histological evaluations were performed of fresh control and cryopreserved tissue strips. Two groups were analyzed. In the group of the smaller fragments, the major face measure 2 mm and in the group of the larger fragments, all the faces measure more than 2 mm. Setting: Veterinary School of the Federal University of Rio Grande do Sul and Nilo Frantz Assisted Reproduction Clinic, Porto Alegre, RS, Brazil. Animal (s): One ovary from a Hereford cow. Main results: The percentages of normal follicles in large ovarian fragments cut into 2mm and >2mm slices were 56% and 34%, respectively. The relative risks to obtain normal follicles in the 2mm and >2mm strips after cryopreservation were 0.63 and 0.47, respectively. The comparison of the two relative risks shows significantly (heterogeneity qui square p=0.022) that the effect of freezing on reducing success rate was higher in large tissue fragments that are cut >2 mm. Conclusion(s): The present study shows that there is an increased risk of damage to primary and primordial follicles when the cryopreserved fragment has all its measures larger than 2mm. Key-words: cryopreservation/ovary/ovarian