642 Growth of Deer Antlers 



Virginia deer, hypophysial stimulation of the antlers precedes gonadal stimu- 

 lation by several months. 



Thus pituitary and gonadal hormones interplay in a definite way and se- 

 quence in regulating antler growth. The gonadal hormone probably exercises 

 a direct control in the internal reconstruction and maturation of the bony 

 parts of the antler. As explained in a previous passage, it remains to be dem- 

 onstrated whether it is also directly responsible for the vascular changes which 

 lead to shedding of the velvet. The gonads appear also gradually to inhibit 

 pituitary function, resulting in the eventual cessation of the hypophysial- 

 gonadal cycle by mid- or late winter, with no further manifestation of 

 hypophysial activity until the onset of the next cycle which begins, depending 

 on the species of deer, several weeks or months after the previous antlers have 

 been cast off. This inhibition of the pituitary is also illustrated by the fact 

 that, upon castration of most species of deer after the velvet is shed, the antlers 

 are cast within a month and new antlers are not formed until the following 

 spring at the usual time (Caton'"). In similarly castrated roe deer, the antlers 

 are likewise immediately shed, but, contrariwise, growth of the permanent 

 castrate or wig antlers begins at once (Rorig^*), indicating that in this species 

 the pituitary has not been fully inhibited. The tremendously rapid and ex- 

 uberant growth of wig antlers in the roe deer, as compared with the lesser 

 growth of castrate antlers in other deer, also suggests that the pituitary in this 

 species is either relatively more potent in its antler-growth-promoting action 

 or is less inhibited by the testes. 



In connection with the possibility of light stimulating the hypophysis of 

 deer, the data of Schumacher™ are interesting. From the observation of roe 

 deer, over many years in the Austrian Alps, he ascertained that their antlers 

 were larger and better developed in those years in which the incidence of 

 sunlight was greater. He concludes that sunlight should be regarded as the 

 most important, although not the only, factor responsible for good develop- 

 ment of the antlers. He believes that sunlight, activating vitamin D, is re- 

 sponsible for the vigorous growth of the antlers in good years. He overlooks, 

 however, the additional possibility of the direct response through neural cen- 

 ters of the hypophysis to light. Other factors, including the abundance or 

 scarcity of food, are also said to exert an influence on the size of the antlers 

 (Caton,'' Seton,'^ Jacobi," Anthony''). 



Other aspects of the periodicity of antler growth and of the reproductive 

 cycle fit into the concept of the role of the hypophysis and testes proposed 

 above. There is a law governing antler growth, based upon the experience of 

 numerous observers (Caton,'" Murie,"* Jacobi," Seton," Brehm,'" Rorig,'' '") 

 to the effect that the more sexually mature and vigorous the animal, the earlier 

 in a given season the antlers begin to grow (giaph 1). Thus the antlers of a 

 six- or eight-year-old healthy buck put in their appearance some weeks earlier 

 than those of the two- or three-year-olds. Similarly the velvet is shed sooner 



