Canine Spermatozoa—Predictability of Cryotolerance

Abstract

Markers of freezability allow the selection of ejaculates of good freezability. So far, most investigations were conducted in boars, bulls, rams and horses, with high economic interests triggering the efforts. The progress in dogs is comparably slow. A critical evaluation of the methods requires consideration of practicability, with most labs not even possessing a computer assisted sperm analyser (CASA); furthermore, small canine ejaculates mostly do not allow the use of large semen volumes. In dogs, modern markers of freezability no longer assess single membrane constituents or seminal plasma components but comprise tests of cell functionality and adaptability, energy metabolism, cluster analyses of kinetic and morphometric parameters, as well as DNA intactness. Identification of the most efficient combination of tests seems useful. At present, examination by CASA combined with cluster analysis of kinetic subgroups, JC-1 staining and COMET assay or staining with toluidine blue seem most appropriate; however, cell volumetry and other functional tests deserve better attention. A better understanding of spermatozoa energy metabolism might reveal new markers. This review focuses on the requirements and markers of freezability of canine semen, highlighting potential future candidates.

Diagnostic tests in canine andrology - What do they really tell us about fertility?

“…Nevertheless, in the light of new emerging technologies and markers [98] we can expect that diagnostic procedures and tests will shed new light into stud dog fertility in the near future. Regarding the possibilities of systems such as CASA, further research is required to determine which measurements are of clinical importance in canine andrology [91].…”

Molecular Biomarkers of Canine Reproductive Functions

“…Therefore, cholesterol in sperm cells provides protection against sperm damage induced by freeze/thaw processes [ 199 ]. Canine sperm membranes are not highly sensitive to cold damage due to their relatively high cholesterol:phospholipid ratio and the PUFA content of the membrane [ 200 ]. Schäfer-Somi and Palme (2016) [ 25 ] showed that in dogs, higher concentrations of cholesterol are found in the seminal plasma of ejaculates with good freezability than in the seminal plasma of ejaculates with bad freezability.…”

“…Ca 2+ levels are low in freshly ejaculated cells; however, during capacitation, Ca 2+ levels increase due to the influx of extracellular calcium ions over the sperm plasma membrane after the opening of voltage-gated calcium channels [268]. Calcium ionophore is a substance that enables the transport of Ca 2+ ions across the spermatozoa membrane by forming stable complexes with divalent cations [200]. Szász et al, (2000) [269] suggested that Ca 2+ -ionophore-induced membrane changes in dog sperm cells are valuable parameters for predicting the suitability of dog ejaculates for cryopreservation.…”