Sperm chromatin structure and sperm morphology: their association with fertility in AI-dairy Ayrshire sires.

Prognostic relations between sperm variables and sire fertility are yet elusive. A retrospective analysis of sperm morphology and chromatin stability (studied using sperm chromatin structure assay [SCSA]) and their relation to fertility after AI (as proportions of 60 days of nonreturn to estrous [NRR], corrected NRR, or calving rate) was studied with preselected frozen semen doses from a group (N = 43) of AI-sires of the Finnish Ayrshire breed composed of 50% subfertile bulls (<55% NRR) and 50% fertile sires (>55% NRR). Fertility, indicated by all three parameters, correlated significantly only with the percentage of morphologically normal spermatozoa, a variable which negatively correlated with the percentage of DNA fragmentation at the time of SCSA, thus confirming the value of always having high numbers of morphologically normal spermatozoa in AI-doses.