DO FARMED DEER HAVE MORE NON-TYPICAL ANTLERS?

George A. Bubenik, (M.D., Department of Zoology, University of Guelph)

This article was originally printed in the February / March issue of Deer Tracking
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Function of antlers.

Deer antlers are often called "luxurious head ornaments", similar to peacock feathers or lion's manes. Antlers indicate the strength and the physical quality of their bearer and their architecture, size and structure is usually species-specific. Although antlers are occasionally used as weapons, their main purpose is to "impress" the females and other males and to help them to establish a higher rank. In addition antlers may function as dispersals of pheromones, hormone-like chemicals produced by various scent glands of the body.

Antler development.

Antlers are deciduous bony protuberances growing from pedicles, the permanent outgrowth of the frontal bones, developing during puberty. Antlers are the fastest growing tissues in mammals, which in elk and reindeer are elongating at the phenomenal speed of more than 2 cm (3/4 inch) per day. Various hormones, enzymes, neurotransmitters and growth factors promote this fast growth. Developing antlers are called velvet antlers, as a specialized type of skin, which resembles velvet, covers their bony core. The antler cycle is regulated by photoperiodicity and the most prominent hormone involved in the seasonal growth and development of antlers is a male sex hormone testosterone (T).

Trauma and antler growth.

Velvet antlers are provided with a vigorous blood supply and exhibit tremendous concentration of nerves, which make them very sensitive to touch. Because of this sensitivity, deer are trying to avoid any contact with the velvet antlers, which would damage their delicate structures. Unfortunately, accidents damaging antlers sometimes happen, such as in cases when a deer is running to escape the danger or if it is hit by hooves of another deer. Minor wounds, such as scrapes or cuts heal quickly without lasting effects on the final shape of antlers. Conversely more extensive injuries, such as those causing subcutaneous bleeding or splitting of the main beam or tines will often result in malformed antlers, called non- or atypical. The most damaging trauma, such as fractures of the pedicle, beam or a tine may result in "monster" antlers that often resemble size and shape of another deer species. Antler malformations resulting from trauma in one year have the tendency to occur in several sets of antlers grown in subsequent years. That happens even if no additional injuries to velvet antlers will occur. As a rule, the earlier the growing stage of antlers, the more malformed antlers develop as a result of trauma. Furthermore, the more malformed are the antlers, the longer the malformation persists, sometimes for many years. It appears as if the deer remembers the trauma.

Antler growth centers.

Because of some similarities with the process of memory, my late father, the prominent deer researcher Anthony (Tony) B. Bubenik, proposed to call this phenomenon of remembering the trauma, "trophic memory" (the memory for growth). He hypothesized that the deer brain has two "antler growth centers" (AGC), one for each side. These AGC are basically independent, but are usually synchronized, working in a tandem. Therefore, antlers usually grow in a mirror image, at the same speed and are cast at the same time. Stress or trauma may influence each AGC differently and then a desynchronization may occur in speed of antler growth and the timing of casting. The AGC has an inborn encryption that determines the species-specific shape and the size of antlers. A trauma to growing antlers, which is registered via numerous nerve endings in the velvet alters semipermanently this encryption. Unlike other memories, the trophic memory is not a mental process but a somatic one. It can be compared to a memory for the production of antibodies to a specific illness, which is initiated by vaccination or an exposure to the disease. It was observed, that small, but repeated trauma (such as a damage to tips of tines) acts synergistically and may prime the AGC to respond vigorously to a subsequent injury. Similarly to a memory process, a trauma sensitizes the brain's AGC to "remember" the shape of antlers resulting from an injury. It is this altered memory that "guides" the antler growth of the subsequent antler cycles to produce malformed (atypical) antlers. As both AGCs are interconnected, the malformed shape of antlers, developed as a result of injury in the previous antler cycle, will simultaneously occur on both sides and will often persist for years.

Antler growth centers and testosterone.

AGCs are influenced by testosterone. It has been hypothesized that the first substantial increase of T during puberty stimulates AGCs which in turn initiate the growth of pedicles. If a male deer is castrated before puberty, he will never grow antlers. Conversely, once the pedicles are formed and the first antlers are developed, castration does not prevent growth of antlers. Because of the lack of T in castrates, these antlers will stay permanently in velvet. During the regular antler cycle, high blood concentrations of T during the rut stimulate AGCs. The intensity of such stimulus is then "remembered" throughout the winter and via brain nerves determines the shape and the size of antlers in the following antler growth period. Therefore, if a buck or stag acquires a high rank during the rut, his antlers will become bigger. Conversely a defeat in the rut or a deterioration of a physical condition, which results in lowering of T concentrations, causes a decrease in antler size the following spring. The lack of stimulation of AGCs in castrates over several years results in progressively sluggish growth, often in atypical shapes. If a deer castrate is treated with T, his antlers will mineralize, be cast, and the shape and speed of antler growth in the next antler cycle will be restored. Trauma versus testosterone. An injury to pedicles can substitute for T stimulation. An accidental trauma initiated accessory antler growth in non-typical places on various bones of the skull (Fig.1). In addition, a unilateral antler growth was induced by trauma to a pedicle developed in a female deer with blocked ovarian function (Fig.2) or in females, which were given a small dose of T. The profound effect on the shape and size of antlers in deer whose pedicles or antlers were damaged during the early developmental stages indicates that trauma is an equivalent to T stimulation of AGCs.

Atypical antler growth on deer farms.

Do non-typical antlers occur more often on deer farms? As the density of deer is much higher in deer farms than in natural conditions, the probability of undesirable trauma or stress is also higher. In addition, large, more elaborate antlers grown as a result of trauma need extra energy that is often not available to wild deer. Finally, deer on farms are genetically selected for the maximal production of velvet antlers with multiple tines, thus predisposing them to respond more vigorously to any external stimulus. Therefore, large, non-typical antlers with a great number of tines will probably occur more often on deer farms and will persist for a longer period of time than perhaps in the wild.

Case histories.

In order to illustrate the process of development of non-typical antlers I will present a few examples of that phenomenon. These were observed and photographed on my white-tailed deer research farm in Cruikston Park, near Cambridge, Ontario.

1) Billy was found as a fawn in 1973 and was brought up on our deer research station. At the age of 2 he was an average 6 pointer of unremarkable size and weight. At the age of 3 he split his left antler just after the initiation of growth. The injury, incurred when he was recovering from an experimental immobilization, resulted in the formation of a double beam (Fig.3). The effect of this injury persisted in the 4th year as a malformation of the prong and the growth of a few supernumerary tines. In the 5th year, during a regular monthly blood sampling, the budding right antler was split again, now into three parts. This time, the antlers responded vigorously to the trauma by producing non-typical antlers with a great number of tines and a massive formation of antler bones (Fig.4). Although all the injuries occurred only on one side, the malformation (a split into three beams) developed also on the opposite site. In his 6th year of life, despite his average body size, Billy produced again huge antlers, which resembled more the antlers of red deer than white-tailed deer. The total weight of Billy's antlers that year exceeded 5 kg (11 lbs) and the main beam had a circumference the size of my forearm. In the 7th and the 8th year, the antlers were still atypical with massive developments of "royals" at the top of the beams. The antlers from the 9th year exhibit a decline in the antlerogenic capacity but even in his final year, 10 years old Billy still produced impressive antlers of a remarkable size. Billy died shortly after he polished his antlers in the fall of 1983. He broke his neck by trying to free himself from being stuck in the fence. The mineralization of antlers, which shifts calcium from the skeletal bones, probably weakened his vertebrae, which were then not strong enough to resist the vigorous jerking movement of Billy's head. He was found paralyzed by the fence and had to be sacrificed.

2) Alpha, son of Billy, was born on our deer farm in 1978. As he was the strongest and the most assertive of our fawns born that year, I decided to call him Alpha. During the first year of his life, Alpha produced "button antlers", signs of a strong antlerogenic potential. Also his true first and second antlers were of very good quality. At the beginning of the third antler cycle Alpha tried to escape from his pen, got his head stuck under the sliding door and trying to free himself, he was scared by a student who rushed to help him. Alpha jerked his head and broke his right pedicle with the attached antler bud. The wound healed relatively quickly but the regeneration of the pedicle took almost the whole antler growth period. That season Alpha ended up with only about 2.5 cm (1 inch) long antler grown on the weakly regenerated right pedicle. The left antler was also much smaller than expected. In the next spring the tiny right antler was cast, including the pedicle (Fig.5). Again the wound healed quickly and a new antler began to grow at a remarkable speed. At one point, the antler on the injured side was more than 3 times longer than the one on the intact side (Fig.6), thus indicating the independence of the AGC, which was stimulated by the injury, suffered in the previous year. As a result, the right antler grew very large, producing a remarkable number of tines. The left antler eventually caught up with the speed of growth of the right antler and as it is usually the case, it also developed a large number of points, almost matching the size of the uninjured antler. The number of true points on both sides is disputable (as some were rather small) but I counted at least 53 (Fig.7). The antlers lost a substantial part of the species-specific shape, looking partly as antlers of reindeer. In the following three years the antlers of Alpha still exhibited malformations (Fig.8), as they slowly returned to a normal shape.

3) Milan was one of the most durable deer I ever had. Despite repeated immobilization for blood sampling (at one point biweekly for 2 years), he was never seriously ill. His body weight and antler size was always superior to most other deer. Milan's T concentrations during the rut were the highest I ever measured in a captive buck. He was always very aggressive, sometimes attacking me with his front legs after casting the antlers. When Milan reached his 8th year, the shape of his antlers began to change from a very typical to a non-typical one. Two years later, when I found him dead from broken neck (he got stuck in the fence during the rut, like Billy), the shape of his antlers was really bizarre (Fig.9). The loss of the species-specific shape in an over-age deer is common to most cervid species. Some of them (surviving to a super old age in captivity) end up bearing single spike antlers. Similarly to a fading memory of old folks, the trophic memory gets extinguished, reverting antlers to a simple shape of yesteryears.

Acknowledgement: The excellent technical collaboration of Ian Smith as well as the editorial revisions of the text by my wife Ella Bubenik, are gratefully acknowledged.

References:

Bubenik A.B. 1990. Epigenetical, morphological, physiological, and behavioral aspects of evolution of horns, pronghorns, and antlers. In: Horns, Pronghorns and Antlers, G.A.Bubenik and A.B.Bubenik, eds., Springer Verlag, New York, N.Y., pp. 3-113.

Bubenik G.A. 1990. Neuroendocrine regulation of the antler cycle. In: Horns, Pronghorns and Antlers, G.A.Bubenik and A.B.Bubenik, eds., Springer Verlag, New York, N.Y., pp.265-297.

Bubenik G.A. 1990. The role of the nervous system in the growth of antlers. In: Horns, Pronghorns and Antlers, G.A.Bubenik and A.B.Bubenik, eds., Springer Verlag, New York, N.Y., pp. 339-358

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