Prognostic value of canine frozen-thawed semen parameters on in vitro sperm–oocyte interactions

Combining the data from conventional semen analysis with oocyte penetration assays should improve the assessment of the fertilizing ability of a semen sample. Thus, the objective of the present study was to evaluate the prognostic value of various semen parameters on the in vitro interactions between frozen-thawed canine sperm and homologous oocytes. Ten ejaculates from five stud dogs (two ejaculates/dog) were collected by digital manipulation. Semen samples were evaluated, extended in Tris–egg yolk–glycerol, frozen and stored in liquid nitrogen, and thawed several weeks later. Samples were evaluated for motility and sperm populations by computer-aided semen analysis (CASA), plasma membrane integrity (carboxy-fluorescein diacetate and propidium iodide), and sperm morphology (Bengal Rose). Thawed spermatozoa were also incubated with homologous oocytes for 18 h in an atmosphere of 5% CO 2 and 95% air at 38 °C and sperm–oocyte interactions were evaluated. Simple linear regression models were calculated, with sperm parameters as independent variables and sperm–oocyte interactions as the dependent variable. There were significant associations between: percentage of oocytes bound to spermatozoa and beat cross frequency (BCF; R 2 = 63%); percentage of oocytes that interacted with spermatozoa and BCF ( R 2 = 73%); and number of penetrated spermatozoa and velocity average pathway (VAP; R 2 = 64%) and velocity straight line (VSL; R 2 = 64%). Although plasma membrane integrity and sperm morphology had little prognostic value for in vitro interactions between canine frozen-thawed sperm and homologous oocytes, some motility patterns (evaluated by CASA) were predictive of in vitro sperm–oocyte interactions.