Dear Ondrej,

Hi, I studied *Croyopreservation and acrosome reaction of dog spermatozoa" in my PhD Thesis (2000, Bristol-UK), using "TRIS-citric acid-fructose based extender" with 20% egg yolk. A brief answer to your question would be that I do NOT think that the outcome of using raw/fresh egg yolk or CEY at the same volume would be the same. It is the actual concentration of the yolk (the contents of *lecithin*, albumin, vitamins, etc) that is more important rather than the volume itself only. Please note that canine semen could be extended up to 1:8 (semen:extender) in TRIS-based extender, without any (*marked*) harmful "dilution effect". If you do not freeze the sperm following dilution, the volume of the yolk could be reduced down to 5-10% (v/v). But, if you freeze the extended semen afterwards, higher actual (raw) yolk content (20%) would be more favorable on the cryosurvival. The question of "whether the nature of egg yolk (in raw or clarified form) matters for the viability of sperm cells, as to be frozen or not" is of scientific concern. So, it would be quite interesting to see the results of both yolk forms to be used along with TRIS-based extender. Please be cautious that the yolk material (of hen's egg) should be as fresh as possible (daily use, if possible) and be kept in the fridge (at +4  degrees C). Surely, antibiotics (of choice, e.g. "Pen. + Strep.", etc) have to be added to the extender routinely. Good luck. Omer

Dear Omer,

thank you kindly for answer. I agree with you, that volume of CEY and EY is no the SAME thing. However, we have performed some experiments with this and different possibilities, now it is in evaluation phase.

Thank you.

My best regards,

Ondrej

Good luck dear Ondrej. I keep waiting to hear about your interesting results. All the best.