Antler Developement

 Antlers

There is something magical and mystical about deer antlers. Part
 of their allure is that every antler is different and unique. However, our
 fascination with deer antlers has its roots deep in our psyche, from our  
 ancestors, who have hunted antlered game since man's existence. Our       
 ancestors used antlers for tools and in religious ceremonies. Today, we   
 are still captivated by antlers.                                          
                                                                           
                                                                           
 Antlers are one of nature's most remarkable accomplishments. The speed at 
 which antlers grow, also makes them the fastest growing structures in the 
 animal kingdom.                                                           
                                                                           
                                                                           
 Antler growth in bucks begins when they are fawns. However, buck fawns    
 never grow antlers larger than short "buttons," or pedicles, which on rare
 occasions become hardened. These pedicles then develop into the buck¹s    
 first spike or branched antlers, when he is a yearling (1 1/2 years old). 
 Antler size then continues to increase each additional year until peaking 
 generally at age 6 1/2 or 7 1/2.                                          
                                                                           
                                                                           
 Bucks begin growing their antlers in late-winter or early spring, within  
 weeks of when the previous year's antlers are shed. Antlers grow very     
 slowly at first, but by late-May, antlers are rapidly growing. Antler     
 growth is usually complete by the end of August. The velvet then hardens  
 and falls off during September. The hardened, polished antlers remain     
 until they are shed during December through April, depending on location  
 and management practices.                                                 
                                                                           
                                                                           
 Why Are There Annual Cycles In Antler Growth?                             
                                                                           
                                                                           
 Believe it or not, the 23 degree tilt of the Earth¹s axis is the ultimate 
 cause for the annual cycles in deer antlers. This tilt is what causes     
 Earth's annually recurring seasons. Deer have adapted their physiology and
 behavior to these seasonal changes, including antler growth. The          
 environmental cue that regulates antler growth is the amount of day       
 length, or photoperiod.                                                   
                                                                           
                                                                           
 The physiological cue is the male hormone testosterone. The way this works
 is complicated, but changing day lengths are sensed by the eyes, which    
 send this message, via the optic nerve, to the pineal gland. The pineal   
 gland - a pea-sized organ at the base of the brain - produces many        
 different hormones. One hormone produced is luteinizing hormone, which    
 controls the amount of testoserone produced in the testes.                
                                                                           
                                                                           
 The antler cycle lags behind the changes in day length because the        
 hormonal changes take time. During fall, decreasing day lengths cause     
 melatonin production to increase, resulting in decreased production of    
 both luteinizing hormone and testosterone. Decreasing testosterone levels 
 then cause the antlers to shed. 

                                          
                                                                           
                                                                           
 Antler Shedding                                                           
                                                                           
                                                                           
 In the past, it was believed that deer withdrew to secluded places to shed
 their antlers in order to avoid the loss of virility in 'public.' However,
 it is likely that deer are unaware of when they will lose their antlers.  
 Antlers are shed when a thin layer of tissue destruction, called the      
 abscission layer, forms between the antler and the pedicle. This layer    
 forms as a result of the decrease in testosterone. As the connective      
 tissue is dissolved, the antler loosens and is either broken free, or     
 falls off on its own. This degeneration of the bone-to-bone bond between  
 the antler and the pedicle is the fastest deterioration of living tissue  
 known in the animal kingdom.                                              
                                                                           
                                                                           
 In whitetails, a restricted diet has been found to cause bucks to shed    
 their antlers early. It has been suspected that the lack of adequate      
 nutrition somehow effects testosterone output. Nutritionally-stressed     
 bucks may also grow their antlers and shed their velvet later. Older-aged 
 bucks are thought to shed their antlers earlier than younger bucks. It has
 also been reported that higher-ranked (more dominant) bucks cast their    
 antlers sooner than lower-ranked (subordinant) bucks. Older-aged, more    
 dominant bucks probably shed their antlers sooner because of the high     
 energy costs incurred in maintaining a higher dominance rank.             
                                                                           
                                                                           
 The farther deer are from the equator, the more defined their antler      
 cycle. In other words, northern deer have a shorter "window" of when      
 antler shedding can occur, compared to deer herds in southern states. In  
 addition, the specific date when a buck will shed his antlers may be      
 determined more by his individual antler cycle than any other factor. This
 cycle is independent of other bucks and is believed to be centered on each
 animal's birth date.                                                      
                                                                           
                                                                           
 Penned deer studies have allowed scientists to measure the exact dates of 
 antler shedding for individual deer year after year. One study in         
 Mississippi found that individual bucks usually shed their antlers at the 
 same time each year and almost always during the same week. Yearling bucks
 with only spike antlers shed sooner than yearling bucks with forked       
 antlers, likely because they were more nutritionally stressed than        
 fork-antlered bucks. This study also indicated there was no relationship  
 between antler mass and date of antler shedding, although other studies   
 have shown that bucks shed their antlers earlier as they grow older.      
 Additional penned studies have also revealed that bucks usually shed both 
 antlers within three days of each other.                                  
                                                                           
                                                                           
 Although there is no clear evidence that weather directly affects antler  
 shedding, it is likely that severe winters may also cause bucks to shed   
 their antlers earlier than normal because of the nutritional stress this  
 causes.                                                                   
                                                                           
                                                                           
 Why Do Bucks Shed Antlers?                                                
                                                                           
                                                                           
 We have examined the environmental and physiological changes that occur to
 cause bucks to shed their antlers every year, but we still haven't        
 addressed the question of why bucks shed antlers. Why do bucks spend so   
 much energy in growing antlers, only to shed these antlers a few months   
 later, forcing them to reinvest an enormous amount of energy to regrow the
 antlers again the following year? Why don¹t deer antlers stay attached and
 continue to grow throughout life like the horns of sheep, goats, and      
 cattle?                                                                   
                                                                           
                                                                           
 Scientists have pondered these same questions for many years and they     
 still do not know the answers. However, several theories have been        
 developed to explain why antlers are shed every year. One of the most     
 common theories is that bucks shed their antlers annually so that they    
 have the potential to replace any damage to antlers that may have occurred
 in the form of broken tines, or a broken main beam. This theory seems     
 valid because antlers are extremely important in display for acquiring    
 females and because they are used during dominance fights with other      
 bucks. If a buck breaks a main beam and is not able to replace that       
 antler, it may not be able to acquire future breeding privileges.         
                                                                           
                                                                           
 A second related theory suggests that bucks shed antlers annually so that 
 they can regrow larger antlers the following year, in order to keep pace  
 with their increasing body size. This theory is based on the fact that    
 antlers quickly mature into nongrowing structures before the buck is able 
 to attain full body size.                                                 
                                                                           
                                                                           
 A third theory states that antlers are shed simply because of an accident 
 of evolutionary chance. In other words, there is no real reason why       
 antlers are shed. Antlers are different from horns, not because they need 
 to be, but because of different evolutionary origin. A fourth theory      
 suggests that antlers are shed in order to stop the die-back process, that
 occurs at the junction of the pedicle and antler, from traveling down into
 the skull.                                                                
                                                                           
                                                                           
 Another theory suggests that antler shedding developed in the primitive   
 antlers of ancestral deer from temperate zones. Antlers of deer in these  
 colder climates would have been vulnerable to freezing in winter if they  
 were not shed. The only way to prevent freezing would have been to stop   
 the blood supply to antlers before the onset of winter.                   
                                                                           
                                                                           
 It is thought that ancestral males shed their antlers so that they were   
 able to mimic the healthier, nonantlered females. In theory, this reduced 
 their vulnerability to predation, because predators may have actively     
 searched for antlered males due to their weakened condition.              
                                                                           
                                                                           
 One final theory simply suggests that antlers are shed each year as an    
 energy-conserving measure, so that males don¹t have the added weight from 
 the antlers to carry outside of the breeding season. Antlers are          
 cumbersome and energy-expensive structures that are not needed after the  
 breeding season. However, for this to be true, it must also be true that  
 regrowing the antlers each year is less energy-expensive than maintaining 
 the antlers through winter. (By Dr. Mickey Hellickson )                                                 

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