Influence of semen collection method on sperm cryoresistance in small ruminants

Abstract

Semen collection for cryopreservation is a key step for small ruminant conservation programs. While in these species semen is mainly collected via artificial vagina (AV), electroejaculation (EE) provides a viable alternative for untrained males. Herein we investigated the effect of semen collection method on post-thaw sperm quality by comparing two small ruminant species, sheep and goats. Semen from Blanca-Celtibérica bucks and Manchega rams was collected by AV and EE on the same day and cryopreserved using a standard protocol. At thawing, sperm motion parameters were evaluated by CASA, whereas membrane stability (YO-PRO-1), sperm viability (propidium iodide, PI) and mitochondrial activity (Mitotracker Deep Red) were analyzed using flow cytometry. The semen collection method negatively affected post-thaw sperm quality in bucks but not in rams. Thus, in bucks, post-thaw sperm motility was higher for samples collected by AV as compared to those obtained via EE. Similarly, post-thaw sperm parameters evaluated by flow cytometry were worse for buck samples collected by EE than those collected by AV in the same species, or than ram samples regardless of collection method. These results suggest that ovine and caprine spermatozoa have a different response to the cryopreservation process depending upon the semen collection method used. We hypothesize that the EE procedure may lead to changes in the composition of the ejaculate in bucks that would make spermatozoa more susceptible to the cryopreservation process, whereas this procedure would have had no effect on ram spermatozoa. This assumption requires further investigation.