Abstract: This invention relates to a DNA sequence comprising at least part of a porcine zona pellucida PZP-4.alpha. or -4.beta. gene coding for an amino acid sequence represented by SEQ ID NO: 1 or SEQ ID NO: 2, respectively, in SEQUENCE LISTING.This invention also relates to an expression system and to expression of said DNA.In addition, this invention relates to an immunogenic recombinant polypeptide or peptide which comprises at least part of said amino acid sequence and which is obtained by expressing said DNA, and to a contraceptive vaccine for use in human or other animals which comprises said polypeptide or peptide as an active ingredient.