Relationships between computerized measurements of motion of frozen-thawed bull spermatozoa and fertility

A computerized system (CellSoft, CRYO Resources, Ltd.) was validated using video tapes of frozen‐thawed bull spermatozoa diluted in filtered (0.2 μm) egg yolk‐citrate extender (8 × 106 spermatozoa/ml) and analyzed at 30 frames/sec for the percentage of motile spermatozoa (≥ 20 μm/sec) and linear velocity of motile spermatozoa. Virtually all motile spermatozoa were detected and debris rarely were classified as immotile spermatozoa if the extender had been filtered. Variation about the mean for percent motile cells was similar when only 12 rather than 20 or 30 frames/field were analyzed. Use of 20 frames/‐ field was adequate to determine the percentage of motile bull spermatozoa. Five mixtures of live and killed spermatozoa were analyzed (four bulls) to evaluate accuracy. Percent motile spermatozoa was correlated (r = 0.97) with the ratio of live:killed spermatozoa. Mean linear velocity of motile spermatozoa was similar for each mixture (P > 0.05). To further evaluate accuracy, percent motile spermatozoa was determined by computer and by “track motility” (20 samples; 0 to 63% motile spermatozoa); values were correlated (r = 0.95). The system was precise (CV of 6% based on triplicate analyses of the same samples) and reasonably accurate for evaluating bull sperm motility if the extender had been filtered and 20 to 25 fields (≥ 200 spermatozoa) were evaluated. Correlations between measurements of sperm motion and fertility were studied using cryopreserved semen from two fertility trials. For the first, 75‐day nonreturn rate data for 20 samples of bull semen (10 bulls) were not significantly correlated with evaluations made by CellSoft. For the second fertility trial, the competitive fertility index (a measure of relative fertility) for nine bulls was correlated (r ≥ 0.68; P < 0.05) with percent motile spermatozoa, linear velocity and straight‐line velocity. Multiple correlations based on six characteristics evaluated by CellSoft, at 0 or 1.5 hours, and the competitive fertility index were ≥0.94. Based on the latter data, the system may facilitate prediction of the relative fertility of bull spermatozoa.