Concentrations of insulin-like growth factor-I in adult ž / male white-tailed deer Odocoileus irginianus : associations with serum testosterone, morphometrics and age during and after the breeding season

Ž . Our understanding of insulin-like growth factor-I IGF-I in cervids has been limited mostly to its effects on antler Ž . Ž . Ž . Ž development in red deer Cer us elaphus , roe deer Capreolus capreolus , fallow deer Dama dama , and pudu Pudu . puda . Although IGF-I has been found to play a critical role in reproductive function of other mammals, its role in reproduction of deer is unknown. The objectives of the present study were to determine if serum levels of IGF-I change during the breeding season, assess whether age influences serum IGF-I, compare levels of IGF-I measured during and following the breeding season, and determine if IGF-I is associated with body and antler characteristics in free-ranging Ž . adult, male white-tailed deer Odocoileus irginianus . We collected serum and morphometric data from hunter-harvested and captured white-tailed deer to investigate these objectives. Mean level of serum IGF-I during the breeding season Ž . was 63.6 ng ml and was greatest in deer between 2.5 and 5.5 years old 57.4 79.9 ng ml . Levels of serum IGF-I decreased by approximately 40% as the breeding season progressed, but levels were less in deer following the breeding Ž . season 34.6 ng ml . Both body and antler size were associated positively with IGF-I when controlling for age. Serum testosterone was also associated positively with IGF-I. Levels of serum testosterone during the breeding season Ž . Ž . generally increased with age from 4.82 1.5 years old to 18.79 ng dl 5.5 years old , but decreased thereafter. These data suggest that IGF-I may be an important hormone in breeding, male white-tailed deer. 2001 Elsevier Science Inc. All rights reserved.