Not sure if it applies here, but in Cordova, Alaska, they have a large portion of the local moose population that grows double main beams. This herd was transplanted and Fish and Game has studied this condition and found it to be genetic in nature. Since the herd was started with so few animals they think one of the original bulls had a genetic condition with his pedicles which is the bone the antlers grow attached to. Evidently when the moose that have this condition drop their antlers, part of the pedical actually breaks off instead of the antler just falling off. Then when the new antler grows, it causes a deformation which many times turns into a double main beam. Can create some real trophies.