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Why Do Moose Shed Their Antlers?

Male moose—the world's largest deer—go to great lengths to allure females.

While humans will soon be spring cleaning, moose clean house in the winter by getting rid of their antlers.

We found out quite a lot about the process when Gaia Restrepo asked: “Why do moose shed their antlers every year?”

Lose Weight Fast

Cattle, sheep, and goats keep and grow their horns, which are made of bone and keratin.

But members of the deer family—including its biggest member, the moose—annually shed their antlers, which are not fused to their skull. Only male moose have antlers, and their growth is regulated by testosterone, Kris Hundertmark, a wildlife ecologist at the University of Alaska Fairbanks, says via email. (Read how moose get so big eating plants.)

Casting off these massive structures frees moose of up to 60 pounds of weight, allowing them to store more energy for the winter, says Lee Kantar, moose biologist with the Department of Inland Fisheries and Wildlife in Maine. Moose are native to cold, northern climes of North America, Europe, and Asia.

Moose “like to push those antlers against each other for dominance,” but since they're not weapons, the animals can afford to ditch them after breeding season, Kantar says. (Related: "Two Bull Moose Found Frozen in Alaska With Antlers Locked.")

During breeding season, though, antlers can be alluring.

"The guy who has the biggest set of antlers and can show them off to potential girlfriends will be the fortunate individual who does the breeding," says Vince Crichton, retired wildlife biologist and moose expert.

How to Make an Antler

Each spring, usually in April, antler bone begins to grow inside a nourishing skin covering on the moose's head, called velvet due to its short, soft hairs.

Moose Loses an Antler

Antlers are "one of the fastest-growing tissues of an animal," adds Kantar, and Crichton has seen up to eight inches of antler growth in a span of nine days.

As testosterone surges in male moose, around September, the velvet will shed (see video) and the antler bone hardens. As males age, their antlers grow in bigger each year. (Also read: "What's a Ghost Moose? How Ticks Are Killing an Iconic Animal.")

If a bull is castrated or the testes don’t descend before the antlers harden, the velvet will remain and the antlers may grow into "odd shapes," Hundertmark notes.

Sexy Scent

Velvet stays on antlers for just over four months, when males will start rubbing up against trees and bushes to remove it—a behavior that turns their antlers brown.

Around late September to early October, bulls will dig a "rutting pit," into which they’ll urinate and then splash urine on their antlers—a scent that induces cows to ovulate.

Getting rid of their antlers, or antler casting, typically happens in early December.

Cells called osteoclasts break down bone cells that attach the antler to the skull, while osteoblasts will start building them up in the spring.

Bulls are in their prime around 10 years old, after which their antler size begins to decline, Crichton says.

No worries, Bullwinkle! We all know that size doesn’t matter.