The sperm heads of frozen/thawed horse spermatozoa were injected into ovulated mouse oocytes where they decondensed and formed paternal pronuclei in which the DNA damage has been evaluated. The motile spermatozoa exhibit none or minor level of DNA damage and the xenogenic zygotes cleave to the two-cell embryonic stage with regular nuclei and no micronuclei (MNs). On the other hand, the immotile spermatozoa exhibit typically high levels of DNA damage and blastomeres in two-cell stage embryos contain multiple MNs. Moreover, extremely high sperm DNA damage prevents even the cleavage to the two-cell stage.Keywords: keyword 1; keyword 2; keyword 3 (List three to ten pertinent keywords specific to the article yet reasonably common within the subject discipline.)