Progress on the role of olfaction in maternal recognition and its signaling mechanism in sheep

Maternal behavior of domestic animals refers to the behaviors related to delivery and rearing of offspring, including nesting, delivery, grooming, recognition, lactation, rearing and protection of the young. These behaviors can provide rich social experience and survival skills for young, which are important for the continuation of species and population stability. Maternal recognition of the young is the first step in the initiation of maternal behaviors, such as lactation, nurturing, and protection. Ewes can quickly and exclusively recognize their lambs after giving birth and establish a strong mother-young bond. The 4-6 h period after delivery is particularly important because it is the critical period for ewes to recognize their lambs, in which olfaction plays a key role. The main olfactory system, which consists of the olfactory mucosa and the main olfactory bulb, and the accessory olfactory system, which consists of the vomeronasal organ and the accessory olfactory bulb, can mediate ewes' recognition and memory of lamb odors. A systematic summary of the olfactory signaling mechanisms is lacking. Given that the high mortality rate of lactating lambs due to poor maternal behavior is a challenge in the farming industry, a systematic review and summary of the role of olfaction in maternal recognition in sheep is particularly important for improving maternal behavior and lamb survival. Here, we reviewed the role of olfaction in maternal recognition in sheep, as well as the structures and functions involved in maternal recognition of the main and accessory olfactory systems. The cAMP signaling pathway mediated by G protein (Golf)-AC3-cAMP and the IP₃ signaling pathway mediated by (OTR)-Gq-PLC-IP₃ have been considered as the main pathways involved in olfactory signaling in the main olfactory system. The olfactory signaling function in the accessory olfactory system is mediated by the G_αi2/G_αo -PLC-IP₃/DAG pathway. It would offer a theoretical reference for further understanding of the olfactory signal transduction mechanism of maternal recognition and maternal behavior improvement strategies.