Olfaction communication plays a significant role in maternal recognition of terrestrial mammals.Precocial species(ungulates) rapidly and selectively recognize and form bonds with their offspring by olfactory cues during the immediate postpartum period,which may be a sensitive period for establishing maternal recognition.Parturition experience,release of oxytocin and nitric oxide contribute to underlying the selective recognition of offspring within sensitive period.Contrast with precocial species,many studies have confirmed that establishment of maternal recognition is based on the familiarity from cohabitation with pups before weaning in altricial species(e.g.rodents).They can not rapidly develop a specialized maternal recognition and bonding with pups after parturition.Recognition between own and alien pups does not necessarily ensure discriminative maternal care.Experimental technique and standard of assessing recognition are critical for studying maternal recognition in rodents.Shortly after birth,mothers of primates,including humans,are capable of forming an early maternal recognition by the scent of their newborn infants.Processes of pregnancy and parturition induce a high state of plasticity of the olfactory system,which may facilitate maternal olfactory learning in mammals.It is also possible that hard-wired perceptual processes are involved in maternal recognition.