Morphologically distinct sperm subpopulations defined by Fourier shape descriptors in fresh ejaculates correlate with variation in boar semen qualityfollowing cryopreservation

This study investigated two hypotheses: 1) that consistent between-boar var iation in frozen semen quality exists and is genetically determined, and 2) that morphologically distinct subpopulations of spermatozoa exist within f resh boar ejaculates and that the incidence of these subpopulations is corr elated with semen quality following cryopreservation. Five ejaculates were collected from each of 15 boars (5 boars from each of 3 breeds). An objecti ve sperm morphology analyzer used Fourier shape descriptors to describe var iation in the morphology of 300 spermatozoa per ejaculate before freezing, Semen was diluted into a commercial freezing buffer (700 mOsm/kg, 3% glycer ol) and 5 straws (0.5 mL) per ejaculate were cryopreserved (to -5 degreesC at 6 degreesC/min, then -5 degreesC to -80 degreesC at 40 degreesC/min). Se men was assessed for percentage of motile cells and motility characteristic s (with computer-aided sperm analysis), plasma membrane integrity (SYBR-14 positive), and acrosome integrity (fluorescein-labeled peanut agglutinin po sitive). Consistent between-boar variability was detected for post-thaw spe rm motility (P < .01), membrane integrity (P < .01), acrosome integrity (P < .01), curvilinear velocity (P < .01), straight-line velocity (P < .05), b eat cross-frequency (P < .05), and amplitude of lateral head displacement ( P < .01). Three morphologically distinct subpopulations of spermatozoal def ined by Fourier descriptors, were detected, The proportion of these subpopu lations within the fresh ejaculate correlated with semen quality assessment s made following cryopreservation. These findings support the hypothesis th at consistent interindividual variation in sperm freezability is geneticall y determined and may relate to processes that occur during spermatogenesis, Subsequent characterization of these genetic differences between "good" an d "poor" freezers may ultimately identify biophysical components of the spe rmatozoa that are essential for successful cryopreservation.