Prolactin inhibition does not influence horn growth in two wild caprinae species: European mouflon (Ovis orientalis musimon) and Iberian ibex (Capra pyrenaica)

Abstract

Studies on seasonal horn development and the endocrine mechanism regulating its pattern in wild ruminants are scarce. The aim of this paper was to study the influence of photoperiod and prolactin (PRL) on horn growth in two wild ruminant species: the European mouflon and the Iberian ibex. Eighteen male ibexes and 13 mouflon rams, maintained in captivity, were divided into three groups: a control group, kept under a natural photoperiod (latitude, 40°25′ N); a long-day group, exposed to an artificial photoperiod of 15-h light and 9-h darkness; and a group treated with bromocriptine (BCR; 10 mg twice weekly during spring and summer) to induce hypoprolactinaemia. Horn length growth (HLG) was recorded weekly for 18 months; plasma PRL concentrations were measured twice monthly by radioimmunoassay. In the ibexes of the long-day group, the period of strong horn development during spring–summer was significantly reduced by 2 months compared with the controls. In the mouflons of the long-day group, this same period was significantly increased by 9 months. In the BCR-treated animals, hypoprolactinaemia was observed in both species, but HLG was the same as in the corresponding controls. The present results suggest that the seasonal pattern of horn growth of wild ruminants is primarily modulated by photoperiod in a species-dependent manner. The persistence of resurgence of horn growth during spring in the BCR-induced hypoprolactinaemic animals of both species suggests that annual variations in blood PRL concentration have no effect on seasonal variation in horn growth.