Allonursing in Wild and Farm Animals: Biological and Physiological Foundations and Explanatory Hypotheses

SIMPLE SUMMARY: Allonursing and allosuckling are behaviors displayed by some females, characterized by nursing and feeding non-filial offspring. Although both are costly behaviors, this type of communal parenting is widespread in various species; however, not all animals display this behavior, and even among species, some differences can be observed. This review aims to analyze the biological and physiological foundations of allonursing and allosuckling in wild and farm animals. It also summarizes some current hypotheses to explain these behaviors as a strategic approach for the mother or the offspring, describing the individual and collective advantages and disadvantages and their implications on an animal. ABSTRACT: The dams of gregarious animals must develop a close bond with their newborns to provide them with maternal care, including protection against predators, immunological transference, and nutrition. Even though lactation demands high energy expenditures, behaviors known as allonursing (the nursing of non-descendant infants) and allosuckling (suckling from any female other than the mother) have been reported in various species of wild or domestic, and terrestrial or aquatic animals. These behaviors seem to be elements of a multifactorial strategy, since reports suggest that they depend on the following: species, living conditions, social stability, and kinship relations, among other group factors. Despite their potential benefits, allonursing and allosuckling can place the health and welfare of both non-filial dams and alien offspring at risk, as it augments the probability of pathogen transmission. This review aims to analyze the biological and physiological foundations and bioenergetic costs of these behaviors, analyzing the individual and collective advantages and disadvantages for the dams’ own offspring(s) and alien neonate(s). We also include information on the animal species in which these behaviors occur and their implications on animal welfare.