Immunolocalization of c-Fos, ELOVL5 and oestradiol in the ewe vulva in relation to oestrus behaviour after treatment with lipopolysaccharide.

Sudden activation of the stress axis by a lipopolysaccharide endotoxin (LPS) significantly reduces ewes' sexual attractivity to rams by delaying all signs of oestrous behaviour. To understand mechanisms involved in attracting male interest, we examined c-Fos (nuclear activation), ELOVL5 (enzyme involved in pheromone synthesis) and oestradiol receptors (ER) using immunohistochemistry on ewe vulval tissue at 0, 31 and 40 hr in the ovarian follicular phase with or without exposure to LPS at 28 hr (5 groups of 4 ewes per group). While there was intense staining for immunoreactive (IR)-c-Fos and IR-ELOVL5 in the vulval epithelium and sebaceous glands, there were no differences in intensity between groups of ewes. The absence of IR-ER staining in vulval epithelium and sebaceous/sweat glands was unexpected. Differences in ram behaviour towards ewes in the ovarian follicular phase and after LPS treatment do not appear to involve quantitative changes in vulval c-Fos, ELOVL5 or ER, but subtle qualitative differences in individual-specific compounds (attraction pheromones) remain an option.