الفهرس 
Introduction
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Abstract
The objective of this study is to evaluate the effect of cryopreservation of cattle oocytes on their fertilizing ability. A total of 5666 oocytes were collected from cattle ovaries. These oocytes were used as: Control oocytes which not exposed to cryopreservation or oocytes cryopreserved at immature or mature stage using one type of four types of cryoprotectants (PROH, DMSO, EG or glycerol) either by vitrification or slow freezing technique. The obtained results revealed that cryopreserved oocytes gave maturation and fertilization rate (45.71; 32.4%, respectively) lower than control one (75 ; 57.1%). On the other hand this study showed that there was a nonsignificant difference between vitrification and slow freezing techniques as methods of cryopreservation. The use of PROH as a cryoprotectant gave fertilization rate (35.2%) higher than other cryoprotectants. Among these groups, it was found that 5.5 and 7M concentration of the cryoprotectants gave best results when the vitrification used as a method of cryopreservation. While on using slow freezing technique 1.5 and 3.5 M concentration of cryoprotectant gave the best result. It could be concluded that there was no so much difference between vitrification and slow freezing techniques as methods of cryopreservation, PROH gave maturation and fertilization rates higher than other cryoprotectants. Moreover concentrations of 1.5 and 3.5 M of the cryoprotectants are suitable on using slow freezing technique while 5.5 and 7 M are suitable on using vitrification one.