Ask a question to an AETA certified ET practitioner

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Published on: February 18, 2021

By Pat Comyn

Ask an ET-related question. An AETA-certified practitioner will answer!

Here’s one I asked Dr. Reuben Mapletoft to answer regarding proper or best thaw temperature for direct thaw (DT) embryos.

Question: Reuben, is there any data that support a 28 to 29°C thaw versus a 35 to 37°C thaw? I see that Japanese papers and the Food and Agriculture Organization of the United Nations recommend 37°C. And how about a 5-s air thaw versus right in bath? It seems to me that cracked zona concerns are a question mark as it hopefully cracks anyhow.

Answer: You are correct; with a direct transfer a cracked zona is probably even preferred. The air thaw is only important for glycerol where it is important to be able to find the embryo.

We looked at several thaw temperatures between 25 and 35°C several years ago and found no difference in survival. I suppose you argue that perhaps you should be thawing near environmental temperature, but I think it is important to thaw quickly. Having said that, thaw rate to 0°C is probably the same for all temperatures, so then the thaw temperature really determines where it ends up.

Reuben J. Mapletoft

Distinguished Professor Emeritus

Department of Large Animal Clinical Sciences

Western College of Veterinary Medicine

University of Saskatchewan Saskatoon, SK S7N 5B4 

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