Ram sexual pheromone: first approach of chemical identification

A series of experiments has been designed with the aim of identifying the pheromone of the ram responsible for the primer effect--induction of a LH peak and ovulation--in anoestrous ewes. In a first experiment, the pheromonal activity of various sources was tested, extract of ram fleece and ante orbital gland secretion induced characteristic changes in LH secretion, whereas urine was ineffective. A second experimental series showed that an accurate separation of the ram's fleece extract in acid and neutral fractions resulted in each case in a complete loss of activity whereas both together were efficient, indicating that the pheromonal action involves several components. From GC-MS analysis of both fractions, and after comparison of male and female wool extract, semi-synthetic formulations were tested. The association of synthetic 1,2-hexadecanediol and 1,2-octadecanediol with the natural acid fraction was efficient in stimulating LH release in anoestrous ewes. As the most frequent linear fatty acids have been shown not to be necessary, a role of branched and oxygenated fatty acids has been hypothesised.