INTERRELATIONSHIPS AMONG FLUOROMETRIC ANALYSES OF SPERMATOZOAL FUNCTION, CLASSICAL SEMEN QUALITY PARAMETERS AND THE FERTILITY OF FROZEN-THAWED BOVINE SPERMATOZOA

Cryopreserved spermatozoa from 8 bulls were used to examine the interr elationships among flow cytometric spermatozoal quality assessments an d classical semen quality parameters and nonreturn rate estimates of f ertility. The integrity of the sperm cell membrane and the functional capacity of the mitochondria were quantified by flow cytometry after c oncurrent staining with carboxydimethylfluorescein diacetate (CDMFDA), propidium iodide (PI), and rhodamine 123 (R123). For each sample a to tal of 10,000 stained spermatozoa were simultaneously quantified for t he intensity of their green and red fluorescence. Three straws from ea ch bull were each examined initially and following incubation at 37-de grees-C for 3 hours to assess the rate of senescence. The proportion o f spermatozoa retaining membrane integrity and having functional mitoc hondria, as determined by CDMFDA and R123 staining, were compared with classical semen quality assessments (sperm motility, acrosomal status , cellular and head morphology, presence of vacuoles/craters and cytop lasmic droplets) and with fertility (nonreturn to estrus rates). For i ndividual ejaculates nonreturn rates, the range was from 61.8 to 78.8% , whereas the cumulative rates of several ejaculates for each bull ran ged from 71.3 to 83.5%. The proportion of spermatozoa with functional membranes and mitochondria were positively correlated with the percent age of spermatozoa with normal morphology (r=0.82; P=0.01) and motilit y after 4 hours of incubation (r=0.78; P=0.02), but not with the estim ates of fertility. The actual number of spermatozoa per straw staining with CDMFDA and R123 after 4 hours of incubation at 37-degrees-C was correlated with the percentage of spermatozoa with normal morphology ( r=0.73; P=0.04). Multiple regression equations indicated that combinat ions of semen quality measurements could be useful in estimating ferti lizing potential.