Assessment of in vitro sperm characteristics in relation to fertility in dairy bulls

The performance of frozen-thawed spermatozoa from 10 Holstein bulls in a range of in vitro diagnostic tests and the relationship with adjusted in vivo fertility data was determined. The tests included an assessment of motility (subjective and computer-assisted), morphology, concentration, viability, acrosomal and chromatin integrity conducted immediately post-thaw and after swim-up, in conjunction with membrane status (CTC staining) and migration in an artificial cervical mucus. Adjusted in vivo fertility correlated with subjectively assessed post-thaw motility (r = 0.672, p = 0.033), post-thaw straight-line velocity (r = 0.636, p = 0.048), post-thaw sperm morphology (r = −0.762, p = 0.010), post-thaw sperm viability (r = 0.635, p = 0.048), the concentration of spermatozoa after swim-up (r = 0.649, p = 0.042), sperm morphology after swim-up (r = −0.687, p = 0.028), the number of spermatozoa migrating 10 mm into artificial cervical mucus (r = 0.632, p = 0.050) and the distance migrated by the vanguard spermatozoon in artificial mucus (r = 0.701, p = 0.024). A stepwise regression analysis identified tests which, when combined, produced models with a strong correlation (R2 > 0.9) to fertility.