Pronghorns are unique animals, from their family, of which they are the only representative, to their horns, which outer layer they cast every year.
Pronghorns Have Horns, not Antlers
Pronghorns have horns, not antlers, although they shed them annually just like deer or elk. On top of that, their horns are more unusual than most people think.
As the only one in the horned-animal kingdom, the pronghorn has a forking horn, instead of a pointy one, like many other horned animals.
The top point is tipped slightly backward, and the fork in the middle of the length leads to a flat prong from which the animal takes its name.
The makeup of the pronghorn’s headgear is more similar to one of a mountain goat’s rather than a deer’s. The base is made of porous bone marrow, covered by a sheath of keratin instead of porous bone turned dead.
However, the most unusual thing about the pronghorn’s horn is that the sheath comes off every year.
Do Pronghorns Shed Their Horns?
Yes, pronghorns shed their horns, although they don’t cast their whole thing away. They only lose their horns’ outer shell, leaving them with small pointy bones covered in hair.
It makes them one of a kind, as no other horned animal loses their horns or even their outer layers yearly, although some bovids are known to exfoliate them once or twice during their lifetimes.
Instead, most of them grow their horns constantly throughout their lives, making them bigger every year.
In some instances, it makes it easier for hunters to determine the animal’s age, like in bighorn sheep.
Like its very distant cousins, antlered Cervids, pronghorns grow their horns before rutting season and drop the outer layer after it’s finished breeding, usually around November in colder climates, to start the process again for the next season.
Many people believe that the horns grow bigger every year, indicating the age of the animal. However, there is no scientific proof of this theory, just like with mule deer and whitetail deer, as well as elk – bigger headgear doesn’t always mean older animal.
The horn’s outer layer, or old sheath, is usually pushed out by the new growth from underneath and cast away to make space for new growth.
An interesting fact is that female pronghorns can also grow horns (around 70% of them), although never as big as males. They can also shed their horns, but sometimes they can collect a stack for about 2 – 3 years.
When that happens, the horn has layers resembling stacked paper cups.
When Do Pronghorns Shed Their Horns?
Male pronghorns shed their horns after the rutting season is over, usually around November or December, depending on the climate.
In Montana, pronghorns can drop their horns as early as the end of October, whereas, in New Mexico, some male pronghorns hold on to their horns until late December.
During the rut (late August – late October), when the testosterone runs high in the pronghorn buck’s body, the horns start their growth from the live bone.
This happens underneath the existing horn, and when the rut is over, and testosterone levels are dropping, so are the old sheaths of horns.
That exposes the new growth that already started from the core bone (which pronghorn never sheds). From that time, the horns will grow steadily until fully mature in July.
The females that grow horns tend to cast them in mid to late summer.[wd_leadmagnet type=”dressing”]
Why Do Pronghorns Shed Their Horns?
Similar to elk and deer, pronghorns lose their horns after the rut to make space for new growth.
However, while deer are shedding their antlers because of dropping testosterone levels and limiting their energy usage over the cold winter months, pronghorns simply need space for new horns that grow underneath the old ones.
Unlike deer, pronghorns grow their horns through the winter, so the reason for limiting the usage of energy is invalid. They need a relatively mild winter and a lot of grazing and forbs to sustain the growth over the winter.
Similarly, testosterone levels do not directly correlate to dropping the horns. Although there is no precise explanation, one can assume that pronghorns drop their horns to make space for new growth.
Pronghorns don’t grow their horns the same way a bighorn sheep would, building the horn from the base. It means that to make space for new growth pronghorn needs to shed its old horn.
How do Pronghorns Regrow Their Horns?
Early scientists believed that the pronghorn’s horns were created by hardened and compacted hair, and many people still believe this to be true.
The reason behind it is that multiple hairs are protruding from the hardened black surface of the horn and even more covering its base. However, this theory is invalid.
The growth of the pronghorn’s horn is similar to skin growth. The basal layer of the skin rises over the new growth from underneath, the cells becoming flat the closer they are to the surface, losing their nuclei and becoming infused with keratin.
The transparent, keratinized skin layer becomes infused into the layer of the horn.
The process can take around ten months, from the time of losing the outer sheath to the time of fully grown forked horns, measuring about 1″.
The growth usually starts during the rut and well before casting the old horn layers. When the sheath is cast, usually around November in colder climates, it reveals a bony core, around 5.3 inches long, covered with hairy skin, with a hard horn on the tip.
After shedding the outer layer, the real growth begins. The horned tip protrudes from the bone alongside the prong, which usually protrudes about 2 inches from the base.
Between December and March, the growth is rapid, which means the pronghorn buck needs a lot of food and mild winter to sustain the growth.
Although it is usually not as strenuous for pronghorns to grow their horns as it is for deer to grow their antlers, it happens during a more demanding time of year, and lack of proper nutrition can still impact the size of the headgear.
After March, the horns mature from the prong up, but between April and July, there is still enough growth to go through – at the base below the prong.
The horns lengthen, thicken, and harden to prepare for the rutting season in September and October.
There is not enough data to know the process behind the growth of the female pronghorn’s horn.
The females that grow horns have smaller core bones and no prongs, and their horns take less time to develop due to their diminutive size.
They also cast them at a different time of the year, indicating a different time for the beginning of the growth.
Do Pronghorns Grow Velvet Like Deer?
No, pronghorns do not have velvet, but their horns are covered by hairy skin until the growth of a new horn begins after the rut.
Although technically, the velvet is also a hairy skin, the hairy skin covering pronghorn’s horns doesn’t come off like velvet. Instead, it is incorporated into the horn during growth.
It also doesn’t play a major role in creating the new horn as velvet has in creating a new antler, although sebaceous glands may prevent the horn from becoming dry and brittle.
As the new layer is pushed up and keratinizes on top, it hardens and creates the black hard sheath covering the bone. The hair roots are embedded in the inner layer of the skin and move with the growth of the horn, except for the tip and the prong.
It gives the horn a hairy appearance, fueling the old theory of hair being the makeup of the pronghorn’s horn.
Pronghorn is definitely an original animal. It doesn’t fit with bovids or cervids but somehow incorporates their most prominent characteristics.
As the only horned animal with deciduous horns, it resembles more deer than a goat in that matter.
However, the histological makeup of the pronghorn’s headgear is more similar to that of a goat, growing keratin-induced skin rather than porous bone.
O’Gara, B.W., & Matson, G. (1975). Growth and Casting of Horns by Pronghorns and Exfoliation of Horns by Bovids. Journal of Mammalogy, 56(4), 829-846.
Skinner, M.P. (1922). The Prong-Horn. Journal of Mammalogy, 3(2), 82-105.
Lubinski, P.M., & Herren, V. (2000). An Introduction to Pronghorn Biology, Ethnography, and Archaeology. Plains Anthropologist, 45(174), p. 3-11.
Hall, Brian K. (2005). Bones and Cartilage. Developmental and Evolutionary Skeletal Biology, p. 95-102.