All about Antlers

Posted at 3:03 pm October 28, 2010 by Kym Nelson

Indian axis deer with antlers in full velvet.

At the San Diego Zoo Safari Park, keepers have a tell-tale sign of autumn’s arrival: the male deer are sporting some impressive antlers! Antlers are typically seen only on male deer—with the exception of caribou or reindeer, where both sexes grow antlers—and these boys will grow a new set each year! 

Antlers begin to grow in the spring from two circular areas on the skull called pedicles. Growing antlers are made up of a mostly cartilaginous tissue covered in “velvet,” the hairy skin that coats the developing antler and serves as a means of protection and a nutrient supply system. During this time, the antlers are filled with capillaries and nervous tissue, which causes them to be very sensitive but also allows them to grow quickly; some species of deer are capable of adding up to one inch of antler each day! 

Antlers grow throughout the summer, and sometime between August and October they undergo a process called “ossification,” the mineralization of the cartilaginous tissue to hard bone. At this time, testosterone levels are rising as the male deer prepare for the upcoming breeding season, and the velvet is shed from the antler. You will often see deer at the Park rubbing their antlers on trees and exhibit “furniture” in an attempt to help remove the velvet. This can cause the antler to appear as if it is bleeding, but remember that one of the main functions of the velvet is to supply the blood needed for antler growth and development. 

Indian axis deer in hard rack

Once the velvet is removed, the deer is said to be in “hard rack.” Shortly after the deer have come into hard rack, their testosterone levels spike as they enter “rut,” a term used to describe the deer mating season. During rut, males start to spar with one another to determine the dominance hierarchy, ensuring that the largest, healthiest males breed first. Due to the increased risk of injury to other animals in the exhibit, the decision is frequently made to remove the antlers shortly after they have come out of velvet. This is not a simple task, since the deer don’t stand still and allow us to remove their antlers! A date is set far in advance, once the keepers can predict when the deer will enter hard rack. 

A veterinarian anesthetizes a deer by shooting a dart into its hip. As soon as keepers enter the stall with the anesthetized animal, they cover its eyes with a towel to remove any possibility of visual stimulation that could cause the deer to stay alert. Heart rate and respiration rate are continually monitored and oxygen is given. It is also extremely important to keep the deer’s head and neck straight and elevated. Since they are ruminant animals, it is imperative that their head not rest on the ground, as this could cause the animal to regurgitate and could prove fatal! Once the deer is sleeping and under the watchful eyes of the veterinarians, animal health technicians and keepers remove the antlers. 

I know you all are wondering how we remove the antlers. I always wondered the same thing, and my first guess was way off! I always thought that the antlers would be very hard—they are bone after all—and that a power saw would be the way to go. Was I ever mistaken! Because we remove the antlers shortly after they have undergone the ossification process, they are not nearly as a hard as I had imagined. The tool used to remove the antlers is called a gigili saw and is actually a very thin, sharp wire with small handles on each end. The wire is wrapped around the base of the antler, making sure it is below the first tine but above the pedicle, and then a keeper just saws off the antler manually! It only takes about three minutes to saw off an antler, and then you are left with a rough stump. The next step is to file off the tips with a rasp so that there are no rough or sharp points. All told it only takes about five minutes for an antler to be removed, and usually two keepers work in tandem to remove both antlers at the same time. 

Once the procedure is complete, the veterinarian reverses the effects of the anesthetic with a combination of drugs, and the deer wakes up. This can be one of the trickiest points of the procedure. Remember that the head must always remain elevated, so initially the antlers provide great handles to keep the animal in the proper position, but we just cut off our handles! Keepers must hold the head by either the ears or by cradling the chin in our hands while we wait for the deer to wake up. Unlike people, who wake slowly and groggily from anesthetic, a deer jumps to its feet and wants to move quickly. A keeper must ensure that the animal can stand steadily but not be in his way if he comes up running or kicking! 

The antlers do not grow back until the following year, so the deer has just had his weapons removed. The small part of the antler that remains attached to the pedicle runs its natural course and falls off a few months later, making room for the antler growth process to begin again the following year. 

Kym Nelson is a senior keeper at the San Diego Zoo Safari Park. Read her previous post, Black Rhino Calf!

You can follow any responses to this entry through the RSS 2.0 feed. Comments are currently closed. Pinging is not allowed.

5 Responses to “All about Antlers”

  1. Lee in Vancouver says:

    This was such a fascinating article Kym. I just have two questions for you. Since the antlers are now removed does the animal still have the urge to be king of the group or does his testosterone level diminish also? Do the keepers decide who will breed with who and you separate them?

  2. Margaret says:

    Thanks, Kym, for very interesting post. Never knew for sure what happened to antlers during rut, but knew they came off in the end.

  3. Dianna from Ohio says:

    Wow.. I learned something today! 🙂 After reading all of these blogs I have determined that a keepers job is never boring or mundane!! Something new every day!! 🙂

  4. Kym Nelson says:

    #1 Lee in Vancouver

    The removal of the antlers will not affect the testosterone levels of the males. They will still display and even butt heads to establish dominance in the herd, but the threat of injury is much diminished.

    All of the breeding done here is in accordance with the Species Survival Plans, and recommendations for breeding are based on genetics and population numbers. Keepers will use several methods to control reproduction with separation of males being at the top of the list. In some instances, when the genetics of an individual male are already well represented, the veterinarians vasectomize that animal to keep the herd intact but stop breeding.

  5. Vonna - North Carolina says:

    VERY interesting!

    Thanks Kym and those who posted very good questions.