Hélène Vacher

In mammals, olfactory communication between conspecifics is crucial in modulating reproductive function. In anestrous does (i.e. female goats), exposure to hair from sexually active bucks (SAB, i.e. male goats) triggers a luteinizing hormone response that may induce ovulation, the “male effect.” However, the chemicals in buck hair responsible for this effect and the sensory pathways used by the females to detect this information remain insufficiently understood. In this study, we investigated whether sensory cells from the main olfactory epithelium (MOE) and the vomeronasal organ (VNO) of does respond differently to olfactory stimuli from SAB versus wethers (CAS, i.e. castrated bucks) and how this response is influenced by the female reproductive status (breeding season, anestrous, or ovariectomized (OVX)). To explore this possibility, we stimulated freshly dissociated cells of MOE and VNO cells with chloroform/methanol and aqueous extractions from buck hair, and we assessed cell activation using calcium imaging. Regardless of the extraction method, we observed more cells activated by SAB hair compounds than by those from CAS males. More MOE cells from anestrous were activated by both chloroform and aqueous extracts from SAB than MOE cells from breeding season, or OVX does. Most of these responses originated from non-mature olfactory neurons. These findings suggest that females can discriminate buck sexual activity through sensory detection by the MOE and VNO. The increased response in the MOE to SAB hair compounds during the anestrous period suggests that the MOE may play a more significant role in the “male effect” during this period.

In goats, early exposure of spring‐born females to sexually active bucks induces an early puberty onset assessed by the first ovulation. This effect is found when females are continuously exposed well before the male breeding season starting in September. The first aim of this study was to evaluate whether a shortened exposure of females to males could also lead to early puberty. We assessed the onset of puberty in Alpine does isolated from bucks (ISOL), exposed to wethers (CAS), exposed to intact bucks from the end of June (INT1), or mid‐August (INT2). Intact bucks became sexually active in mid‐September. At the beginning of October, 100% of INT1 and 90% of INT2 exposed does ovulated, in contrast to the ISOL (0%) and CAS (20%) groups. This demonstrated that contact with males that become sexually active is the main factor prompting precocious puberty in females. Furthermore, a reduced male exposure during a short window before the breeding season is sufficient to induce this phenomenon. The second aim was to investigate the neuroendocrine changes induced by male exposure. We found a significant increase in kisspeptin immunoreactivity (fiber density and number of cell bodies) in the caudal part of the arcuate nucleus of INT1 and INT2 exposed females. Thus, our results suggest that sensory stimuli from sexually active bucks (e.g., chemosignals) may trigger an early maturation of the ARC kisspeptin neuronal network leading to gonadotropin‐releasing hormone secretion and first ovulation.