The role of olfactory signals in the male effect on small ruminants: an updated overview.

In certain mammals, photoperiodic variations regulate reproductive function, limiting the breeding season to a specific period. In temperate and subtropical latitudes, sheep and goats are considered short-day breeders, with their breeding season typically occurring from late summer to early winter. However, male sociosexual stimuli can override photoperiodic regulation, reactivating female estrus behavior, luteinizing hormone (LH) pulsatility, and ovulation during the anestrous period (i.e., sexual rest) – a phenomenon known as the “male effect” in sheep and goats. Over the last few decades, several investigations have focused on the involvement of various sensory components in the emission, detection, and transduction of the male stimulus in these models. It appeared that olfactory stimuli play a significant role. This review aims to provide an updated understanding of the role of male olfactory stimuli (from rams and bucks) in stimulating female sexual activity (in ewes and does) during the male effect. We will review the evidence regarding the role of these stimuli in this phenomenon, their nature(s), and the involvement of the different olfactory systems (main and accessory). Additionally, we will discuss how to characterize these stimuli and explore future directions related to them.