How Much Do Bighorn Sheep Horns Weigh? Ram and Ewe Horn Facts

How heavy are a ram’s horns?

The commonly cited maximum for a pair of bighorn sheep ram horns is about 14 kg (30 lb). For a ram that weighs 58–143 kg (128–315 lb), that means the horns can make up around a tenth of his body weight or more, all carried on the head.

Not every ram reaches that figure. Horn size depends on age, genetics, food quality and the health of the herd. Young rams have small horns, and the massive full-curl horns seen in photos belong to rams that are usually at least seven or eight years old. Rocky Mountain bighorns in the north tend to grow the largest horns, while desert and Sierra Nevada bighorns are smaller overall.

What are bighorn horns made of?

Each horn has two parts. Inside is a core of living bone, an outgrowth of the skull. Covering it is a thick sheath of keratin, the same tough protein that makes up hair, fingernails and hooves. The sheath grows from the base, pushing older horn outward, so the tip of a ram’s horn is the oldest part.

This layered structure is light for its strength and good at absorbing impact. Rams depend on it in the autumn rut, when they slam their horns together in contests over ewes. See Why do bighorn sheep butt heads?

Growth rings show a ram’s age

Horn growth is seasonal. In spring and summer, when food is plentiful, the sheath grows quickly. In winter growth almost stops, leaving a ring or groove around the horn called an annulus. Wildlife biologists count these annuli to estimate a ram’s age, much like counting tree rings, although the first year or two can be hard to read and worn tips may remove the oldest rings.

The space between rings also tells a story. Wide gaps mean good growing seasons, while narrow ones can reflect drought, a hard winter or poor health. Horns that grew fast early in life often belong to rams from well-fed herds.

Broomed tips

Many older rams have horns that end in blunt, flattened tips instead of sharp points. This is called “brooming.” It comes from clashing with other rams and from deliberately rubbing the tips on rocks. It is often suggested that rubbing may stop the horns from curling so far that they block the ram’s side vision.

Ewe horns

Ewes also grow horns, but theirs are short, narrow and only gently curved, rather like a goat’s. They are useful in minor disputes within the female herd and for defending lambs. Because ewes and young rams both have small horns, it can be hard to tell them apart at a distance; young rams’ horns are usually thicker at the base and begin to curl after the first couple of years.

How do bighorn horns compare with other wild sheep?

Bighorn rams carry some of the heaviest horns of any wild sheep, but they are not the record holders. The argali of the mountains of Central Asia, the largest wild sheep, grows the biggest horns, with spirals that can be considerably longer than a bighorn’s. The bighorn’s northern cousin, the Dall sheep of Alaska and northwestern Canada, has much thinner, lighter, pale amber horns that flare outward in a wide spiral.

Among North American mammals, few animals carry so much weight on the head relative to body size. A bull moose’s antlers can be heavier in absolute terms, but they are shed each winter, while a bighorn ram carries his horns year-round, across cliffs and through deep winter cold.

Horns vs antlers

Horns and antlers are often confused, but they are different structures:

• Horns (sheep, goats, cattle, bison, antelopes) have a bone core with a keratin sheath, are usually found in both sexes, are never branched and are kept for life.
• Antlers (deer, elk, moose, caribou) are made entirely of bone, are usually branched, grow mainly in males (except caribou and reindeer) and are shed and regrown every year. See why deer shed their antlers.

So a bighorn ram carries the same horns his whole life, getting heavier every year. Elk bulls, by contrast, drop their antlers each winter and grow a new set by late summer.

Horns and people

Bighorn horns have long been valued. Native American peoples, including the Shoshone, made bows, spoons and other tools from bighorn horn, and big full-curl horns made the species a prized trophy. Unregulated hunting was one of the reasons bighorn numbers fell sharply in the late 1800s. Hunting is now strictly limited, and in parks such as Yellowstone and Glacier, the horns are best appreciated through binoculars.