 heparin and carbohydrate binding, enables their central role in promoting attachment of the spermatozoa to carbohydrate groups on the glycoproteins found on the surface of oocytes.The spermadhesins from pigs, bulls and stallions show 40-98% similarity in their amino acid sequences and all possess a disulphide bond between adjacent cysteine residues.The porcine spermadhesin polypeptides are coded by five closely linked genes.