Smell, Suck, Survive: Chemical Signals and Suckling in the Rabbit, Cat, and Dog

Abstract

All mammalian young depend for their survival for at least some period on the mother's milk. Locating the mammary region, attaching to a nipple or teat, and being motivated to suck until milk flows is one of the first and most vital challenges they face. For altricial species such as the European rabbit (Oryctolagus cuniculus), the cat (Felis silvestris catus) and the dog (Canis lupus familiaris) born without vision, not directly aided by the mother, and having to compete with litter-mates, the challenge is particularly great. All three species use chemical cues apparently emitted under hormonal control by lactating females to achieve this. From birth they quickly orient to the mother's ventrum, rapidly locate nipples, and respond with nipple-search behavior and nipple attachment to other lactating females but not to non-lactating females. Kittens, but not rabbits or puppies, also quickly establish a nipple order in which each kitten uses primarily one or sometimes two particular nipples. Recognition of own nipples appears to depend on learned olfactory cues, possibly contained in each kitten's own saliva. These three species illustrate similarities and differences in the use of chemical cues by mammalian young in the suckling context and raise questions warranting further investigation: are there commonalities in the origin and chemical composition of the suckling signals emitted by the mothers of such taxonomically different species? Are there commonalities in the neural processing of such signals, for example, in the participation of the main and accessory olfactory systems? To what extent are inborn responses augmented or even replaced by learned chemical cues? And does the early experience of such cues affect the response to chemical signals in later life?