Horn growth related to testosterone secretion in two wild Mediterranean ruminant species: The Spanish ibex (Capra pyrenaica hispanica) and European mouflon (Ovis orientalis musimon)

Seasonal variations in the horn development and testicular activity of the Spanish ibex (Capra pyrenaica hispanica) (n = 6) and European mouflon (Ovis orientalis musimon) (n = 5) were monitored to determine the role of increasing testosterone concentration on the arrest of horn growth during the rutting season. Marked seasonal variations in the rate of horn growth (P < 0.01) and testicular activity (P < 0.001) were seen in both species, although the magnitude and timing of these changes were different (P < 0.01). Horn growth rate was inversely correlated to seasonal levels in testosterone plasma concentration in both species (ibex: R = −0.45, P < 0.01; mouflon R = −0.51, P < 0.01). In the mouflon, the increase in plasma testosterone concentration recorded in September (P < 0.05 compared with the lowest concentration) coincided with a significant reduction in horn growth (P < 0.05). In the ibex, the increase in plasma testosterone concentration in October (P < 0.05 compared with the lowest concentration) was associated with a significant arrest of horn growth in November (P < 0.05). These results appear to support the hypothesis that high peripheral plasma levels of testosterone are linked with the seasonal arrest of horn growth during the rutting period.