Loss of spermatozoa viability following cryopreservation, historically attributed to the formation of intracellular ice, is now believed to be a result of an osmotic imbalance during thawing. Osmotic imbalances result in the movement of water into cells, causing them to swell and burst.

In a recent study co-authored by John Morris, PhD, from Asymptote Ltd., a United Kingdom-based company specializing in controlled solidification, spermatozoa were collected from a single stallion and cooled at various rates ranging from 0.3 to 3000° per minute. Spermatozoa were then analyzed to determine if intracellular ice was present.

“Since research using human spermatozoa and bacteria suggested that spermatozoa were damaged due to an osmotic imbalance during the thawing process, it seemed reasonable to explore this mechanism of cellular damage in horses,” reported Morris.

According to Morris, “No intracellular ice was identified in equine spermatozoa at any cooling rate. Armed with this knowledge, it is now possible to develop new models and cryopreservation protocols that should predict the optimum methods of freezing spermatozoa to improve viability rates upon thawing.”

The successful cryopreservation and subsequent thawing of spermatozoa is important in veterinary medicine to maximize viable spermatozoa on thawing. In addition, cryopreservation of spermatozoa is also important in human medicine and in conservation applications.

The study, “Rapidly cooled horse spermatozoa: Loss of viability is due to osmotic imbalance during thawing, not intracellular ice formation,” was published in the Sept. 15 edition of the journal Theriogenology. Contributing authors were Morris; Faszer, PhD; Green, PhD; Draper, PhD; Grout, PhD; and Foneseca, PhD.