Relationships between serum serotonin, plasma cortisol and behavioral factors in a mixed-breed, -sex and -age group of pet dogs

Previously identified correlations between circulating cortisol and serotonin levels with aggressive, fearful, or impulsive behavior in dogs have led to the suggestion that these measures be assessed as screening tools to aid in the identification of individual dogs with aggressive or fearful tendencies in applied settings, such as shelters or breeding programs. Previous studies investigating relationships between peripheral serotonin or cortisol and behavioral measures have several limitations, including single-breed sample groups, small sample sizes, and inconsistent methods used to collect behavioral data. This study used previously validated questionnaires to investigate relationships between owner-reported histories of dogs' behavior and peripheral cortisol and serotonin measures collected on presentation to a novel environment, in a mixed-breed and mixed-age sample of dogs. No notable relationships were found between these measures in this group, indicating that circulating cortisol and serotonin are poor candidates for use in applied behavioral assessments for mixed-breed pet dogs of varying ages. Differences between results reported here and previous literature are discussed.