The importance of early life experiences for the development of behavioural disorders in domestic dogs

Behavioural disorders are a major reason for euthanasia and sheltering of pet dogs and can be disruptive for the human-animal relationship. The prevention and treatment of behavioural disorders can only be improved by a better understanding of the underlying causes. Early life experiences, such as maternal care, attachment and socialisation, have long lasting and serious consequences for the behavioural and physiological development of an individual. The complex interplay between these factors is likely to have consequences for the vulnerability to develop behavioural disorders. Here, we summarise the current literature on the interactions between maternal care, attachment formation, and the sensitive socialisation period and their potential consequences on adult dog behaviour. Based on the findings we highlight gaps in knowledge and provide suggestions for future research. Background: Aggression, anxiety and separation related behavioural disorders are commonly seen in pet dogs worldwide, with a high impact for the owner and society (Voith, 2009). These behavioural disorders are an important cause for sheltering and euthanasia requests (Lambert et al., 2015). An increased incidence of behavioural disorders such as fear and aggression has been found in commercially bred dogs (McMillan, 2017), and may be caused by a lack of appropriate stimulation during early life (Jagoe, 1994 in Serpell & Jagoe, 1995). In early life, maternal care, mother-pup attachment and the sensitive period for socialisation contribute to shaping the neuronal and behavioural profiles of an individual (Weaver, 2009; Roth & David Sweatt, 2011; Sachser et al., 2013). Proper stimulation during this period is essential for a normal behavioural development, and insufficient stimulation, as well as minimal maternal care and attachment, may increase the risk of developing behavioural disorders. This review aimed at elucidating the complex interplay between maternal care, attachment formation and socialisation, as well as their importance for the development of behaviour and behavioural disorders. To stimulate future research deficits in the current knowledge are highlighted as well. Methods: A literature research procedure was performed using three main search terms: “maternal care”, “attachment”, and “socialisation”. These terms were combined with the terms “dog OR pup OR canine OR canid”, “development”, and “behavioural problems”. The articles that resulted from this search were first selected on whether the research truly involved dogs, but literature proved scarce and so literature on other mammals was also incorporated in the review. References in selected articles were also used, as well as articles that referenced the primary article, which were found using the ‘cited by’ function available in most search engines. Results: The quality and quantity of maternal care appears to affect the behavioural development of dog pups. However, the influence of maternal care on development in rodents is far more extensive and includes physiological development, therefore rodent literature was used to substantiate the limited knowledge on the role of maternal care on development in dogs. Only one study investigated intraspecific attachment in dogs, whereas most literature describes the human-dog bond. Here, human literature was used to extrapolate findings to dogs. The limited evidence available suggests similar attachment styles in dogs as are seen in humans. Literature on the sensitive period for socialisation in dogs is also scarce and largely outdated, but the extensive work that was done on the subject in the 1950s and 1960s is still relevant. Some studies were able to show interactions between experiences during the sensitive period for socialisation and the behavioural outcome of the adult dog. Conclusions: For a normal behavioural development proper social stimulation is required during the sensitive period in early life. Indeed, studies suggest that negative experiences or insufficient stimulation during the socialisation period, as well as minimal maternal care and attachment, increase the risk of the development of behavioural disorders in this species. Unfortunately, our knowledge on the subject is still rather limited and more research into the influence of early life experiences on behavioural development is needed. Societal impact: The sheltering and euthanasia of dogs due to behavioural problems that may very well be preventable by proper stimulation during the sensitive period in early life is primarily an ethical issue. Increasing our knowledge on the influence of maternal care, intraspecific attachment and socialisation on behavioural development could reduce the incidence of behavioural problems such as fear, aggression and separation related behaviour. As a result the number of sheltered and euthanized dogs will decrease. In addition, biting accidents resulting from fear and aggressive behaviour in dogs may decrease. References Lambert, K., Coe, J., Niel, L., Dewey, C. & Sargeant, J.M. (2015). A systematic review and meta-analysis of the proportion of dogs surrendered for dog-related and owner-related reasons.—Prev. Vet. Med. 118: 148-160. McMillan, F.D. (2017). Behavioral and psychological outcomes for dogs sold as puppies through pet stores and/or born in commercial breeding establishments: current knowledge and putative causes.— J. Vet. Behav. Clin. Appl. Res. 19: 14-26. Roth, T.L. & David Sweatt, J. (2011). Annual research review: epigenetic mechanisms and environmental shaping of the brain during sensitive periods of development. — J. Child Psychol. Psychiatr. 52: 398-408. Sachser, N., Kaiser, S. & Hennessy, M.B. (2013). Behavioural profiles are shaped by social experience: when, how and why. — Phil. Trans. Roy. Soc. Lond. B: Biol. Sci. 368: 20120344. Serpell, J. & Jagoe, J.A. (1995). Early experience and the development of behaviour. — In: The domestic dog: its evolution, behaviour and interactions with people (Serpell, J., ed.). Cambridge University Press, Cambridge, p. 79-102. Voith, V.L. (2009). The impact of companion animal problems on society and the role of veterinarians. — Vet. Clin. N. Am. Small Anim. Pract. 39: 327-345. Weaver, I.C. (2009). Shaping adult phenotypes through early life environments.—Birth Def. Res. C: Embryo Today: Rev. 87: 314-326.