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To select rams suitable for ovine in vitro embryoproduction (IVP), the predictive values of the screening tests used toidentify unsuitable rams need to be established. The present study examinedsome characteristics of frozen-thawed ram spermatozoa that might beevaluated routinely in a commercial breeding programme. These included spermmotility, plasma membrane integrity, morphology, and acrosome and capacitationstatus of the sperm population. Cryopreserved spermatozoa from four Dorsetrams, which had previously satisfied the selection criteria for inclusion in acommercial breeding programme, were used for IVP. The overall contribution ofthe four rams and the ejaculates within each ram to the variability(R2) in the production ofblastocysts was very small (2.1% and 2.5% respectively). Theanalysis of the sperm characteristics by logistic regression revealed asignificant and positive association between total post-thaw sperm motility,viability and longevity with in vitro blastocystproduction. However, there was no association between the other surfacecharacteristics of the spermatozoa measured in this study with embryoproduction. Despite the absence of differences between the rams in the lowincidence of polyspermic fertilization, the significant and detrimentaleffects of polyspermic fertilization on in vitroblastocyst production rates were quantified by logistic regression analysis. Alarge proportion of the variability within the IVP system was unaccounted forby the analysis of sperm and oocyte characteristics evaluated in this study.Thus, the identification of other factors contributing to the variability inthe production of embryos in vitro warrants furtherinvestigation. No single sperm characteristic was sufficient to predict theultimate outcome of blastocyst production. Rather, assessments of multiplecharacteristics within the IVP system are required to make accuratepredictions.Extra keywords: fertility, sperm motility. |
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