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

Our understanding of insulin-like growth factor-I (IGF-I) in cervids has be en limited mostly to its effects on antler development in red deer (Cervus 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 repr oductive function of other mammals, its role in reproduction of deer is unk nown, 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 bree ding season, and determine if IGF-I is associated with body and antler char acteristics in free-ranging adult, male white-tailed deer (Odocoileus virgi nianus). 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 was 63.6 ng/ml and was greatest in d eer 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 level s were less in deer following the breeding season (34.6 ng/ml). Both body a nd antler size were associated positively with IGF-I when controlling for a ge. Serum testosterone was also associated positively with IGF-I. Levels of serum testosterone during the breeding season generally increased with age from 4.82 (1.5 years old) to 18.79 ng/dl (5.5 years old), but decreased th ereafter. These data suggest that IGF-I may be an important hormone in bree ding, male white-tailed deer. (C) 2001 Elsevier Science Inc. All rights res erved.