Maternal odor promotes filial vocal search responses, and maternal exposure increases activity in the main olfactory bulb in suckling lambs.

Maternal chemosensory cues are an important component of the ewe-lamb bond, yet behavioral responses to these cues and their neural correlates from the offspring's perspective remain poorly characterized. We hypothesized that own-mother odor selectively promotes filial searching behavior during maternal separation, whereas exposure to the own mother increases neuronal activity within the main olfactory bulb (MOB) in suckling lambs. In Experiment 1, one- and three-month-old lambs were exposed to wool from their own mother, from a familiar mother, or to no wool during mother-young separation. In Experiment 2, one-month-old lambs were exposed to their own mother, to a familiar mother, or to isolation, after which c-Fos immunoreactivity was quantified in the granule cell layer of the MOB, the accessory olfactory bulb (AOB), and the anterior olfactory nucleus (AON). Own-mother wool increased vocal call frequency relative to the no-wool condition at both ages, whereas familiar-mother wool did not differ from either condition. In Experiment 2, lambs exposed to their own mother exhibited higher c-Fos⁺ cell density in the MOB granule cell layer than isolated lambs. Granule-layer c-Fos⁺ density was independent of the duration of sniffing toward the ewe in both treatments. In contrast, neither the AOB nor the AON showed treatment differences in c-Fos⁺ activation. The present study supports a role for wool odors of the mother and for the main olfactory system in processing maternal cues in suckling lambs.