Background: Small ungulates (sheep and goat) display a seasonal breeding, characterised by successive periods of sexual activity (SA) and sexual rest (SR). In sexual activity period the ovarian cycle of females is active and ready for reproduction (oestrus) whereas in sexual rest no ovulation and reproduction are possible (deep anoestrus). Odours emitted by a sexually active male can reactivate the ovarian cycle of anoestrus females. The plasticity of the olfactory system under these hormonal changes has never been explored at the peripheral level of odours reception. As it was shown in pig that the olfactory secretome (proteins secreted in the nasal mucus) could be modified under hormonal control, we monitored its composition in females of both species along several seasons, thanks to a non-invasive sampling of olfactory mucus. Results: In both species the olfactory secretome is composed of isoforms of OBP-like proteins, generated by post-translational modifications, phosphorylation, N-glycosylation and O-GlcNAcylation. Important changes were observed in the olfactory secretome between the sexual rest and the sexual activity periods, characterised in ewe by the specific expression of SAL-like proteins and the emergence of OBPs O-GlcNAcylation. In Goat, the differences between SA and SR did not come from new proteins expression, but from different post-translational modifications, the main difference between the SA and SR secretome being the number of isoforms of each protein. Conclusion: Despite common behaviour, seasonal breeding, and genetic resources, the two species seem to adapt their sensory equipment in SA by different modalities: the variation of olfactory secretome in ewe could correspond to a specialization to detect male odours only in SA, whereas in goat the stability of the olfactory secretome could indicate a constant capacity of odours detection suggesting that the hallmark of SA in goat could be the emission of specific odours by the sexually active male.