Do lactating ewes guide lambs to their teats by smell? Perinatal change in inguinal wax composition and lambs’ reaction to it

Abstract Amongst the array of sensory cues maternal ewes provide to their lambs, the role of odors still remains unclear in Ovis aries . Specifically, the communicatory potential on lambs of the scent released by the ewes’ perimammary inguinal glands is little studied. It is thus worthy to increase our insight about the adaptive value of ovine inguinal glands, the chemical nature of their secretion (i.e., inguinal wax, IW) and their communicative function in the success of initial suckling episodes. A first study explores whether IW from late pregnancy ewes differs from that of postparturient ewes in macroconstituents (lipids, proteins, water) as a proxy to changes in inguinal glands’ activity at the time when lambs’ teat searching and sucking are initiated. Then, the composition in volatile constituents is compared between IWs sampled at both physiological stages using solid-phase micro-extraction of the headspace and gas chromatography-mass spectrometry, allowing to identify 22 odor-active compounds. A second study assessed whether newly-born lambs discriminate the odor of IW from late-pregnancy ewes from that of IW from postparturient ewes (not their own mothers). While late-gestation IW tended to differ from postpartum IW in macroconstituents and in some volatile constituents, lambs seemed to respond indiscriminately in a behavioral test of choice between paired odors although they detected them. Thus, IW of any peripartum ewe (excluding the mother) is potent to elicit olfactory attraction in lambs ahead of the first suckling experience. Ovine IW is therefore in a good position to convey odor cues or a specific chemomessage that guides lambs toward the inguinal-mammary region of their mother.