Impact of extraction method on the quality of bull epididymal sperm

Sammanfattning

Epididymal sperm are a potential resource enabling the preservation of valuable genes in populations where collection of ejaculated semen is not possible. There are many suggested methods on how to extract epididymal sperm, although comparison of some of these and establishment of a gold standard method have not been thoroughly studied – especially not in bovines. In this study the aim was to evaluate and compare two of the most used extraction methods in bulls, evaluating sperm quality characteristics to establish which method is to be preferred. The material used, consisting of pairs of bull testes, was provided by a local abattoir, and the extraction, as well as the initial analysis before cryopreservation, was executed the same day. The sperm collected using the cutting method (A), where incisions are made into the caudae epididymidis and the exuding sperm suspension is collected, had a significantly lower total and progressive motility than the vas deferens retrograde flushing method (B) prior to cryopreservation. This difference also applied to the kinematic parameters curvilinear velocity, straight line velocity, average path velocity and amplitude of lateral head displacement, as assessed by computer assisted sperm analysis (CASA). Another important aspect favoring Method B is that it exhibited a trend towards significance regarding a higher number of spermatozoa obtained, a desirable property when aiming to extract epididymal sperm from genetically valuable individuals. Regarding the flow cytometry analyses plasma membrane integrity, reactive oxygen species and sperm chromatin structure, no differences were detected between the methods. Following the first analyses the samples were cryopreserved and subsequently analysed again after thawing. There were multiple differences between the samples prior to cryopreservation and post-thawing, showing a decrease in characteristics post-thawing for all quality analyses except for the chromatin structure and the reactive oxygen parameter Live SO+. No significant differences or correlations were found in sperm characteristics between the left and right testes, or between scrotal and testicular circumference. A weak correlation with age was, however, discovered implying that older bulls have better sperm motility and viability; the presence of testicular adhesions was associated with impaired sperm quality. All in all, this implies that the retrograde flushing method is to be preferred when extracting epididymal sperm, to acquire a higher total number of motile sperm in the fresh sperm sample. Regarding cryopreservation, a different protocol should be evaluated to achieve better post-thaw sperm quality. One should also bear in mind that sperm quality in younger bulls might not be as good as in slightly older ones.