Why red deer shed their antlers every year

A fully grown stag's antlers look as though they were built to last forever. Yet they fall off every year, and the stag regrows them completely within just a few months. No other mammalian organ is capable of this. Behind this cycle lie daylight, hormones and a remarkable trick: the stag borrows the building material from its own skeleton.

Antlers are not horns

In our region, red deer, roe deer and fallow deer carry antlers, while in the far north moose and reindeer do too. An antler consists of real bone and grows on two bony protrusions of the frontal bone, known as pedicles. The pedicles remain for life, while the antler beams above them are replaced every year. As a rule, only the males carry antlers, with the reindeer being an exception, as the females also grow a set.

Chamois and ibex are quite different: they are horn-bearers. Their horns consist of a bony core with a horn sheath that keeps growing throughout the animal's life and is never shed. This means the age of a chamois or ibex can be read from the annual rings on its horns, whereas this is not possible with antlers.

Light sets the pace

Day length dictates the rhythm. Via the hormone melatonin, it controls the production of testosterone. In red deer, testosterone levels rise in late summer. The antlers then fully ossify, the velvet skin dies off and is rubbed off on shrubs and young trees. During this fraying, the stag often damages the bark of young trees, leaving behind the typical fraying damage.

When testosterone levels drop in red deer in late winter, bone-resorbing cells become active at the junction between the pedicle and the antler. They dissolve the tissue at this junction until the antler breaks off under its own weight. The second antler usually follows within hours to a few days. Casting is a natural process without external force. What remains is a small wound surface on the pedicle that bleeds briefly and is quickly covered over by skin.

A common simplification, which also appears in many infographics, states: the antlers fall off after the rut. For red deer, this is not quite correct. Several months pass between the autumn rut and the casting, and the stag continues to carry its hard antlers throughout the entire winter.

Red deer and roe deer: two different calendars

Red deer

Older red deer cast their antlers in February and March, younger ones as late as April or May. Regrowth begins immediately afterwards, with the strongest growth phase falling in the months of April to July. Velvet is shed in July and August, and the rut follows from mid-September. More on the rut and why hunting takes place precisely at that time can be found in the article on the Valais high hunt and the red deer rut.

Roe deer

For the roe buck, the calendar runs almost in reverse. It casts its antlers, as the small roe deer antlers are called, between October and December, and builds the new ones in the middle of winter beneath the velvet. In spring, roughly from March to May, it sheds the velvet, and the rut takes place in midsummer, in July and August. Anyone who sees a roe buck in winter with furry buds on its head is therefore not witnessing an error of nature, but the normal course of events.

Up to two centimetres a day

Antlers are considered the fastest-growing tissue in mammals. In red deer, the antlers lengthen by up to two centimetres per day during the main growth period, as a review article in Biology Direct (2024) summarises. In the largest antler bearers, the scientific literature cites peak values of up to 2.75 centimetres per day.

During growth, the antler is covered with velvet, a hairy skin full of blood vessels and nerves. It supplies the bone with oxygen and nutrients and is very sensitive. Deer in velvet therefore tend to avoid confrontations, settling rank disputes during this time with their forelegs rather than their antlers.

How a tissue can grow this fast without derailing was investigated by an international research team in 2019 in the journal Science. The result: antler growth makes use of signalling pathways otherwise known from cancer development. At the same time, certain genes in red deer that suppress tumours are under strong selection pressure. The antler is thus a strictly controlled form of extreme growth and is of great interest for research into regeneration and cancer.

Bone on credit from the animal's own skeleton

Roughly half of a finished antler consists of minerals, above all calcium and phosphorus. A red deer cannot take in this much through its diet within a few months. It therefore draws the material from its own skeleton, particularly from the ribs. According to the review mentioned above, over 60 per cent of the minerals in the antler come from the animal's bones.

Experts speak of cyclical, physiological osteoporosis. During antler growth, the red deer's bones become measurably more porous, and towards the end of the growth phase it rebuilds them completely. The fact that a mammal undergoes this bone loss every year and completely reverses it also makes the red deer interesting for human osteoporosis research.

Why does an animal go to this enormous effort year after year? Biologists interpret the annual rebuilding as follows: a broken or damaged antler is replaced after one season, and the new one reflects the red deer's current state of health and nutrition. The antler is thus an honest signal to rivals and hinds.

What happens to the shed antlers

Shed antlers rarely remain untouched for long. Mice, squirrels and other non-human animals gnaw on them, covering their need for calcium and phosphorus. Over the years, the antlers thus disappear into the forest's nutrient cycle.

Less harmless is the hunting of shed antlers by humans. The canton of Grisons states on its page on wildlife refuge areas that these are explicitly aimed not only at winter sports enthusiasts but also at «antler seekers» — people who, from February onwards, search for shed red deer antlers — and in doing so they primarily name recreational hunters. The timing is sensitive: in late winter, the fat reserves of red deer are at their lowest, and every flight through deep snow costs energy that is then missing for survival. The Prättigau municipality of Grüsch therefore issued nighttime access bans in 2018 and 2019, partly because of antler seekers, with fines of up to 3,000 francs. Anyone out in the forest in winter should respect wildlife sanctuary zones and leave shed antlers where they lie.

Comment: A gift that no one needs to shoot for

The red deer sheds its antlers naturally every year. Not a single animal has to die for this. And yet, in recreational hunting, the antler is still regarded as a trophy to be earned with a rifle. At trophy shows such as in Thun antlers are measured and awarded prizes, and cases such as the illegally killed royal stags of Amden show just how far the greed for a large antler can go.

The biology of the antler itself shows exactly what is lost in this process. A strong antler is the result of good health, nutrition and age. Anyone who specifically shoots the red deer with the largest crowns removes precisely those animals from the population that make their quality visible. In bighorn sheep on Ram Mountain in Canada, it has been shown that decades of intensive trophy hunting have led to measurably smaller horns. Our article explains why killing for the sake of physical features cannot be ethically justified: «Trophy hunting: What lies behind killing as a status symbol?».

An antler is a marvel of regeneration. It belongs on the head of a living red deer or, as a shed antler, in the cycle of the forest — not on the wall of a living room. Further background on wild animals and their biology can be found in the section Education.

Frequently asked questions about antler shedding

Does shedding its antlers hurt the red deer?

Shedding is not a violent tearing off. Bone resorption releases the antler at a prepared separation point, and the wound surface heals quickly.

When do red deer in Switzerland shed their antlers?

Red deer shed between February and May, with older animals doing so earlier than younger ones. Roe deer bucks shed between October and December.

How long does it take for a new antler to grow?

In red deer, growth from shedding to a fully developed, polished antler takes around five months.

Is it permitted to simply take shed antlers home?

This is regulated differently from canton to canton. Regardless, the following applies: wildlife sanctuary zones may not be entered in winter, or only on designated routes, and deliberately searching for shed antlers disturbs the red deer during the most energy-sapping time of the year.