The present invention provides isolated nucleic acid molecules that encode asubstantial part of canine RANKL polypeptide, including the extracellulardomains of that polypeptide, the polypeptide and fragments thereof. Vectorsand host cells encoding and expressing canine RANKL polypeptide are provided,as well as antibodies that bind to RANKL and that inhibit RANKL activity. Alsoprovided are methods of treating an animal to inhibit or treat the loss ofbone minerals.