PORCINE SPERM FERTILIZING POTENTIAL IN RELATIONSHIP TO SPERM FUNCTIONAL CAPACITIES

Fertile males vary in the fertilization efficiency of their sperm, but these differences are not readily detected with the currently routine in vitro semen analyses. Inseminating females with mixed semen contai ning equal numbers of sperm from two males, heterospermic insemination , is an efficient means to detect these differences in vivo. In this s tudy, heterospermic insemination procedure was used to estimate relati ve in vivo fertility of the nine pairs of ejaculates from 12 fertile b oars. In vitro assays that model various steps in the fertilization pr ocess were used to estimate the contribution of various steps in the f ertilization process to the variation in sperm fertilizing potential. These assays included sperm binding to the porcine zona pellucida (ZP) , acrosomal status in conjunction with viability before and after capa citation, interaction with the hamster oocyte plasma membrane and char acteristics of sperm motion. The ejaculates exhibited significant vari ation in sperm fertilizing potential as assessed by the heterospermic insemination procedure. The ability to interact with the oocyte plasma membrane was significantly correlated with relative in vivo fertility (R(2) = 0.80; P < 0.005); the other functional characteristics of the se samples were not correlated with in vivo fertility. The lack of cor relation between in vivo sperm fertilizing potential and some of the f unctional characteristics such as motility is likely a reflection of t he very limited variation in these characteristics in fertile males. T he high correlation between in vivo fertility and ability of porcine s perm to interact with hamster oocyte plasma membrane suggests assessme nt of this interaction may improve the in vitro assessment of sperm fe rtilizing potential.