Preventing physical interactions between parturient ewes and their neonate differentially impairs the development of maternal responsiveness and selectivity depending on maternal experience

The present study investigated whether deprivation of nursing or of any physical interaction with the lamb impairs the onset of maternal responsiveness and the establishment of selectivity in primiparous and multiparous ewes. Just after parturition, ewes could interact freely with their lamb, or could only lick their lamb but not nurse them, or could neither lick nor nurse them for the first 4 h. At 4 h, mothers were successively observed for 3 min with an alien lamb and then with their own lamb. Only 5/14 primiparous mothers accepted their own lamb following deprivation of all physical contact whereas all multiparous mothers did so (19/19). Also, deprivation of all physical contact resulted in a significantly higher proportion of multiparous mothers accepting an alien lamb (6/18) than following deprivation of nursing only (0/19) indicating an impairment in selectivity. Finally, there was no indication that preventing only nursing led to a deficit either in maternal responsiveness or selectivity, neither in primiparous nor in multiparous ewes. These findings underline the importance of perception of olfactory cues from amniotic fluids through licking and/or physical contact and interacting with the lamb for the development of maternal responsiveness and selectivity.     

Evidence for cell proliferation in the sheep brain and its down-regulation by parturition and interactions with the young

Production of new neurons continues throughout life in the subventricular zone (SVZ) and the dentate gyrus (DG) of the hippocampus and is influenced by both endocrine and social factors. In sheep parturition is associated with the establishment of a selective bond with the young based on an olfactory learning. The possibility exists that endocrine changes at parturition together with interactions with the young modulate cell proliferation in the neurogenic zones. In the present study, we first investigated the existence of cell proliferation in sheep. Newly born cells labeled by the cell proliferation marker 5-bromo-2′-deoxyuridine (BrdU) were found in the SVZ, the main olfactory bulb (MOB) and the DG and completely co-localized with Ki-67, another mitotic marker. Forty to 50% of the BrdU-labeled cells contained GFAP suggestive of the presence of neural stem cells. Secondly, parturition with or without interactions with the lamb for 2 days, down-regulated the number of BrdU-labeled cells in the 3 proliferation sites in comparison to no pregnancy. An additional control provided evidence that this effect is specific to early postpartum period: estrus with interactions with males did not affect cell proliferation. Our results provide the first characterization of neural cell proliferation in the SVZ, the DG and unexpectedly in the MOB of adult sheep. We hypothesize that the down-regulation of cell proliferation observed in the early postpartum period could facilitate the olfactory perceptual and memory demands associated with maternal behavior by favouring the survival and integration of neurons born earlier.     

Sensory and physiological determinants of maternal behavior in the goat (Capra hircus)

Maternal behavior in the goat appears at the time of parturition, partly under the activating influence of vaginocervical stimulation. Mothers actively lick their neonate and rapidly establish a selective bond with their kid through olfactory recognition. They also develop visual and acoustic recognition of the kid within 4 h following birth. Acoustic recognition is present at 48 h. The establishment of maternal recognition can be impaired by underfeeding during the second half of pregnancy. There is no indication that the mechanisms controlling the onset of maternal behavior and bonding are different from those reported in sheep, despite the fact that lambs start to follow their mother within a few hours after birth and kids hide for about a week. During lactation, the cues provided by the kid are necessary for the maintenance of maternal responsiveness, but suckling itself does not appear of primary importance. The presence of the kid also modulates the hormonal response to udder stimulation and influences recovery of postpartum sexual activity when kidding (i.e. birthing) takes place in autumn. Finally, the rapid establishment of mutual attachment between mother goats (does) and their kids offers the possibility to investigate an aspect of mother-young affiliation that is not present in many laboratory species.