Human neonates prefer colostrum to mature milk: Evidence for an olfactory bias toward the “initial milk”?

Abstract

Objectives Colostrum is the initial milk secretion which ingestion by neonates warrants their adaptive start in life. Colostrum is accordingly expected to be attractive to newborns. The present study aims to assess whether colostrum is olfactorily attractive for 2‐day‐old newborns when presented against mature milk or a control. Methods The head‐orientation of waking newborns was videotaped in three experiments pairing the odors of: (a) colostrum (sampled on postpartum day 2, not from own mother) and mature milk (sampled on average on postpartum day 32, not from own mother) (n tested newborns = 15); (b) Colostrum and control (water; n = 9); and (c) Mature milk and control (n = 13). Results When facing the odors of colostrum and mature milk, the infants turned their nose significantly longer toward former (32.8 vs 17.7% of a 120‐s test). When exposed to colostrum against the control, they responded in favor of colostrum (32.9 vs 16.6%). Finally, when the odor of mature milk was presented against the control, their response appeared undifferentiated (26.7 vs 28.6%). Conclusions These results indicate that human newborns can olfactorily differentiate conspecific lacteal fluids sampled at different lactation stages. They prefer the odor of the mammary secretion ‐ colostrum ‐ collected at the lactation stage that best matches the postpartum age of their own mother. These results are discussed in the context of the earliest mother‐infant chemo‐communication. Coinciding maternal emission and offspring reception of chemosignals conveyed in colostrum may be part of the sensory precursors of attunement between mothers and infants.

Testing detectability, attractivity, hedonic specificity, extractability, and robustness of colostrum odor—Toward an olfactory bioassay for human neonates

“…It conveys an odor factor that carries salient "signal" value (sensu Sokolov, 1963) and induces automatic appetence movements. This general result is in line with the recent finding that total colostrum odor elicits active attraction behavior in waking 2-day-olds, actualized in positive head-turning (Klaey-Tassone et al, 2021).…”

“…(1) Its detectability and attractivity are measured against a scentless control stimulus (water); already evidenced with paired-choice tests in waking infants (Klaey-Tassone et al, 2021), the detectability of colostrum odor is further verified here in different conditions of infant state and stimulus delivery;…”

“…It is thus important to characterize human mothers' evolved strategies to pilot their neonates to suck for colostrum, relying on neonates' keen somato-and chemo-sensation. The present study is an additional step (Klaey-Tassone et al, 2021;Le Roy et al, 2022) toward finding out whether the vital mammary substrate available only the first few days after birth conveys an attractive/appetitive chemosignal.…”

Olfaction in the Multisensory Processing of Faces: A Narrative Review of the Influence of Human Body Odors

“…Olfaction is a sensory channel benefiting from an early start as nasal chemosensation is functionally operative from the periphery to the brain by the end of the second gestational trimester (Schaal, 1988;Schaal et al, 2004;Browne, 2008). The partial overlap between the chemical profile of colostrum/milk secretions and that of the amniotic fluid allows for an olfactorilysmoothed natal transition continuity between intra-uterine and extra-uterine life (Schaal et al, 2020), notably through the exposure to colostrum, mother's breast and body odor (Schaal et al, 2004;Marlier and Schaal, 2005;Klaey-Tassone et al, 2020). Such chemosensory continuity is essential in the adaptive development of other mammalian neonates, and is thought of as laying down the foundation for optimal social-emotional growth and cognitive development in humans as well (Schaal et al, 2020).…”

Olfactory-to-visual facilitation in the infant brain declines gradually from 4 to 12 months

“…The mother’s body odor is a mixture of several compounds conveying a variety of cues about her traits (e.g., identity, femininity, humanity) and states (e.g., maternity, emotions). In particular, certain cues emanating from milk can be discriminated by infants, who differentiate human from non-human milk (Marlier & Schaal, 2005), lactating from non-lactating women (Makin & Porter, 1989), or early from late lactation milk (Klaey-Tassone et al, 2020). Given that young infants are generally more often breastfed than older infants, feeding status is a candidate factor for the maternal odor effect.…”