In both moose and caribou, the calcium and phosphorus demands were so high that animals had to “borrow” these minerals from the other bones in their bodies in order to build their antlers. They could not get enough from their diet, so they pulled calcium and phosphorus from their own skeletons, reallocating them to the antlers. This is truly a form of deficit spending for these animals because it is not sustainable. The depleted skeletal reserves have to be replenished through feeding after the rut, and failure to do so is generally catastrophic. … All told, antlers in these animals turned out to be every bit as costly to a male as reproduction was to a female: the cost of building and using antlers was energetically and nutritionally equivalent to the cost of producing and nursing two fawns to weaning. Antler growth dramatically reduces bone mass overall, rendering males more fragile, more brittle, and much more prone to bone breaking. In essence, antler growth induces a seasonal form of osteoporosis exactly when animals are engaged in the most physically demanding and dangerous activities of their lifetimes.

Emlen, Douglas J, Animal Weapons_ The Evoluti…, loc. 317