The present invention provides isolated nucleic acid molecules that encode a substantial part of canine RANKL polypeptide, including the extracellular domains of that polypeptide, the polypeptide and fragments thereof. Vectors and host cells encoding and expressing canine RANKL polypeptide are provided, as well as antibodies that bind to RANKL and that inhibit RANKL activity. Also provided are methods of treating an animal to inhibit or treat the loss of bone minerals.