Horn sheath growth in Pronghorns is an interesting subject in that they are unique because they are the only ungulate that have horns and that shed the sheath yearly. Their horns are different from the typical horns on ungulates, say for instance the horns on a Bighorn Sheep which continue to grow throughout the life of the sheep, do not have forks and are never shed. Their horns are also different from the antlers of members of the deer family who shed their antlers yearly after the end of rut and they are nearly always forked.
Antlers are made of bone while horns are hollow and composed of keratin, the same as our fingernails.
Pronghorn have different headgear. Each horn is composed of a slender, flattened blade of bone that grows from the front of the skull, that bone forms the permanent core of the horn.
The image above shows a mature Pronghorn buck last December on Antelope Island State Park after he had shed the outer sheath of his horns which we can compare to the third image below of a mature buck during the rut. The horns of the buck above don’t have a fully developed sheath.
The sheath that covers the bony core is a keratinous sheath which is shed and regrown on an annual basis. This past March while I was camping in Wayne County, Utah I found a shed horn sheath at the campsite and photographed it with with my phone. The specimen I found had weathered and almost looked like tree bark. The sheath is hollow and didn’t weigh very much at all, in fact I was surprised by how light it was. The annual new growth of the pronghorn horn sheath actually aids in pushing the old horn sheath off as it grows.
The image above of a mature pronghorn buck was taken during the month of September on Antelope Island State Park during the pronghorn rut, it shows the forward facing single flat prong that is also called the cutter which is not evident in the first image. The horn of this buck has a fully developed sheath. I have never found a shed horn sheath on Antelope Island but I am pretty sure they are there.
I did not keep the shed horn sheath I found in Wayne County because I am not informed about laws concerning shed antlers and horn sheaths. Besides it belongs on the windswept sagebrush steppe I found it on.
Pronghorn are the sole living species in its genus Antilocapridae and they are only found in North America so they are as unique as their horns.
Life is good.