Male isolation: a behavioral representation of the pheromonal 'female effect' in donkey (Equus asinus).

The appearance of a decisive component of the sexual response to chemosexual signals in the male donkey was investigated through a comparison of the variations in the time-span of the behavioral classes and units for the natural versus induced breeding seasons. The results demonstrate that there are significant variations in the length of the appetitive sexual behavior (ASB) and consummatory sexual behavior (CSB) under these two reproductive conditions. These differences are analyzed for the ASB, which is adaptable, compared with the stereotyped CSB. For the ASB, male isolation is the most represented behavior of both the natural and induced breeding seasons. This is the key that allows the passage from courtship, which consists of appetitive behaviors, to copula, the consummatory behavior. This isolation appears to provide the time required to activate the hypothalamic-pituitary-gonadal axis through the chemosexual pathway of pheromone stimuli. This isolation is lengthened with induced breeding, supporting the hypothesis of the activation of the neuroendocrine system, which is not 'primed' outside the natural breeding season, and which is necessary to release the stereotyped CSB.