Survival of frozen-thawed sheep embryos cryopreserved at cleavage stages

This study evaluated the effect of freezing-thawing procedures on the viability of sheep embryos cryopreserved at various developmental stages. The survival rates of frozen-thawed embryos were compared with non-frozen counterparts. Embryos were recovered from the oviduct and uterus, at different days of the early luteal phase, and were classified at six different developmental stages 2- to 4-cell (n = 72), 5- to 8-cell (n = 73), 9- to 12-cell (n = 70), early morulae (n = 42), morulae (n = 41), and blastocyst (n = 70). For each early cleavage stage and blastocysts, approximately half of the embryos, were frozen immediately by slow freezing with an ethylene glycol-based solution. The remaining embryos were cultured to the hatched blastocyst stage. All morulae and compact morulae were frozen after recovery with the same protocol. Cryoprotectants were removed using 1 M sucrose solution, and then warmed the embryos were cultured to the hatched stage in a standardized in vitro culture. Embryo developmental stage had a significant effect on the ability to hatch following freezing (P < 0.0001). The cryotolerance of the embryos fitted a regression (r2 = 0.908), increasing linearly from 2- to 4-cell embryos (17.1%) to morula stage (46.3%) and in a quadratic regression from the morula to the blastocyst stage (83.7%). Frozen early cleavage stage embryos had a significantly lower viability than their fresh counterparts (23.1 vs 83.1%; P < 0.0001), with a similar rate of viability between fresh or frozen blastocysts (92.5 vs 83.7%). In conclusion, early sheep embryos are very sensitive to freezing per se and the survival rates following conventional freezing improve as embryo developmental stage progresses. © 2005 Elsevier Inc. All rights reserved.

Bibliographic Details

Main Authors:	Garcia-Garcia, R. M., González De Bulnes, Antonio, Dominguez, V., Veiga-Lopez, A., Cocero Oviedo, María Jesús
Format:	artículo biblioteca
Language:	English
Published:	Elsevier 2006
Subjects:	Cryopreservation, Embryo development, Cleavage stage, Ewe, Freezing-thawing,
Online Access:	http://hdl.handle.net/20.500.12792/5122 http://hdl.handle.net/10261/289682
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