Rank dependent seasonal levels of IGF-1, cortisol and reproductive hormones in male pudu (Pudu puda)

We tested the following hypothesis: when two pudu males share a single pen throughout the year, the dominant animal will have a higher level of IGF- 1 than its subordinate pen mate, particularly during the period of increased social friction (e.g. rut and establishment of territories): To test this hypothesis, we used data from six adult males maintained at the University of Concepcion, Chile (latitude 36.6°S), and analysed them from the males' dominance point of view. Two males plus eight to ten females were kept in one pen and although we did not specifically measure dominance, the rank position was obvious from frequent encounters between the bucks. Three consecutive blood samples were taken monthly over the period of 1 year. In addition to IGF-1, we also analysed seasonal levels of testosterone, cortisol, prolactin, LH and FSH. The analysis revealed that IGF-1 levels of dominant males were significantly higher than those of subordinate males from September to November (the second part of the antler growing period and time of establishing territories). Testosterone levels were higher and FSH levels were lower in dominant males during the rut. Levels of prolactin were higher in dominant animals in November (summer). Cortisol and LH did not show any significant differences between dominant and subordinate males. This data provides the first evidence indicating the possible link between dominance and blood levels of IGF-1. The functional explanation of such links is discussed.