Zona pellucida filtration of structurally abnormal spermatozoa and reduced fertilization in teratospermic cats

Zona pellucida (ZP) penetration, in vitro fertilization, embryo development, and the morphology of fertilizing sperm were examined through use of normospermic (> 60% structurally normal sperm/ejaculate) versus teratospermic (< 40% structurally normal sperm/ejaculate) ejaculates from domestic cats. In addition, the effect of swim-up processing on sperm-oocyte interaction was compared with that of simple sperm washing. Normospermic and teratospermic ejaculates were evaluated for sperm motility and morphology. Sperm were preincubated for 1 h, then coincubated with in vivo-matured follicular cat oocytes (n = 401) for 20 h and with ZP-intact, salt-stored oocytes (n = 202) for 6 h. In vivo-matured oocytes were assessed for percent cleavage and stage of embryo development over time. Salt-stored oocytes were assessed for percent ZP penetration (proportion of oocytes containing sperm within or through the inner ZP), mean (+/- SEM) number of inner ZP-penetrated sperm, and the morphology of all bound and penetrated sperm. The incidence of pleiomorphic sperm in raw ejaculates averaged 29% in normospermic versus 67% in teratospermic males, but all ejaculates contained high sperm motility ratings (> 60%). Swim-up processing increased (p < 0.05) the number of normal sperm recovered/teratospermic inseminate (66.5 +/- 2.3%) compared to recovery after simple washing (28.6 +/- 2.2%). Percent sperm motility also increased (p < 0.05) in teratospermic males after swim-up (90.0 +/- 1.3%) as compared to sperm washing (64.2 +/- 3.7%). Cleavage rate in vitro was higher (p < 0.05) using sperm from normospermic (86.3%) compared to teratospermic (50.3%) males, but rates of embryo development to the morula/blastocyst stage were similar (p > 0.05). ZP penetration of salt-stored oocytes by normospermic ejaculates (73.7%) was superior (p < 0.01) to that of teratospermic ejaculates (24.1%); the number of ZP-penetrated sperm/oocyte was 5-fold higher (p < 0.05) in the normospermic than in the teratospermic group. The proportion of structurally normal bound and ZP-penetrated sperm was similar (p > 0.05) between cat populations regardless of the morphologic forms in the inseminate. Structurally abnormal sperm from teratospermic males were capable of ZP binding (29%) and initial penetration into the outer ZP (17%). However, only 3% of the inner ZP sperm were pleiomorphic, and every sperm within the perivitelline space was morphologically normal. Although swim-up processing increased sperm motility and the number of structurally normal sperm in the teratospermic inseminates, no difference (p > 0.05) was observed in cleavage or ZP penetration. These results indicate that the ZP is an efficient filter for structurally abnormal sperm, but even normal sperm from teratospermic cats appear impaired in fertilizing ability. Although teratospermia compromises ZP penetration and fertilization, the few embryos produced via teratospermic ejaculates develop normally in vitro.