The Science Behind Antler Growth
Bowhunting 360 has published several articles about deer antlers, covering topics such as shed antlers, antler fascinations, antler purposes and terminology, and craft projects that require antlers. This article scientifically explores the annual growth and composition of these miraculous boney crowns that adorn bucks’ heads.
The Growth Cycle
The first step for antler growth is the pedicles, the two sites where antlers connect to the skull. Once a buck is born, the pedicle pushes up until it’s visible on the deer’s head when they’re about 4 months old.
The antler’s growth cycle typically starts in spring when a buck is about age 1. However, large buck fawns born early in the year – around May to early June – might produce small, hardened “buttons” their first winter. Either way, the growth process is the same no matter a buck’s age.
Antlers begin growing from the pedicle as soft cartilage covered by a fuzzy coating called “velvet.” Antler velvet is dense with blood vessels that carry nutrients to the growing antler, and helps protect it from breakage and infections. Spurred by hormones and excess nutrition, antlers grow from March through late August.
Demarais said antlers can grow about 1/8 inch daily for yearlings and about 1/4 inches daily for adult bucks. That’s as much as 1½ inches per week for adults! The growth rate slows dramatically in late summer as antlers mineralize and harden.
When blood stops flowing into the antler velvet, it dries, cracks and falls away. The process usually ends two to three weeks before the autumn equinox in September. Bucks often thrash their antlers against brush and small trees to speed the velvet’s removal, which takes as little as 24 hours.
A buck sports its hardened antlers through January or February, often using them to spar and fight for dominance with other bucks. After the breeding season, around December, cells called osteoclasts demineralize the area where the pedicles meet the antlers, which weakens their “grip.” That process – combined with the antlers’ weight – makes antlers fall off or be “cast.”
Once antlers cast, their pedicle is an open wound that bleeds a short time before scabbing. Antlers begin growing soon after the wound fully heels. Hormone levels, including testosterone, vary by buck and affect their antler growth timeline.
White-tailed deer antlers in their hardened “bone” state are composed of roughly 23% calcium, 10% phosphorus, 0.5% magnesium, 0.8% sodium, 0.3% sulfur, and a combination of iron, zinc, copper, aluminum, potassium, manganese and other elements.
Because antlers change from soft cartilage beneath velvet to hard bone, their proteins, minerals and elements change, too. The antlers’ chemical composition also differs from the base to the tips because of their six-month growth cycle. The nutrients a buck consumes affects its antler composition while each section grows. Generally, antler tips have more protein and minerals than the bases.
Antler composition also varies by region because of differences in diet and soil characteristics.
Typical or Nontypical Antlers
Deer antlers are classified as “typical” or “nontypical.” In general, the tines of typical antlers grow vertically as individual points, whereas the tines of nontypical antlers grow down, horizontally and sometimes fork. Although most bucks grow typical racks, abnormalities that produce nontypical antlers aren’t rare.
Demarais and Strickland said injuries, genetics or health cause most antler abnormalities. Identifying those causes, however, sometimes requires a necropsy, or internal examination, after a buck dies. However, injuries cause most abnormalities, and include pedicle damage, broken rear legs, or damage to a growing antler.
Researchers believe broken bones change the blood supply to the antlers, which causes antlers to grow irregularly. These injuries are said to cause “contralateral asymmetry” problems because they usually affect the antler on the opposite side of the deer’s head. In other words, if a buck breaks its right rear leg, its left antler will likely grow oddly.
Damaged pedicles can also cause abnormal antlers because the pedicle is the source of antler growth. Demarais said older bucks often have injured pedicles and abnormal antlers because they tend to fight more aggressively, which increases their opportunities to damage pedicles.
Velvet antler tips are most susceptible to injury and damaged-induced irregularities because they’re soft. Fractured beams or tines can heal and keep growing as long as the antler receives blood throughout the growing season.
Promote Antler Growth
Can hunters and wildlife managers promote antler growth? Well, here’s the deal.
“Improving antler size is not a ‘quick fix’ operation,” Strickland said. “You can’t pour antlers out of a bag. For long-term results, you must develop a management plan that improves the bucks’ nutrition and allows them to get older.”
Age, nutrition and genetics influence antler development. Managers can only influence a deer’s age and nutrition. Their antlers increase annually until reaching their maximum potential when the buck is 5 to 7 years old. Allow bucks to mature, and their antlers benefit, too, assuming their nutrition promotes antler growth and development.
Strickland said hunters can create relatively inexpensive mineral supplements by visiting most county cooperatives. Use two parts dicalcium phosphate and one part mineralized salt.
Visit the MSU Deer Lab website for more details regarding antler growth and deer-management strategies.