Daily fluctuation of urine serotonin and cortisol in healthy shelter dogs and influence of intraspecific social exposure

The aim of this study was to evaluate the effects of intraspecific social exposure (socialization vs rest) and habituation factors on the levels of urinary serotonin and cortisol [corrected respectively for creatinine to give the serotonin-creatinine ratio (5-HT/Cr) and cortisol-creatinine ratio (C/Cr)] and how they fluctuate in dogs. The frequency of marking during social sessions was recorded to evaluate its relationship with physiological parameters. The effects of covariates on 5-HT/Cr and C/Cr were assessed using a linear mixed models. 5-HT/Cr values were higher at dawn than at dusk during resting days, however, this difference is less evident after socialization sessions. During rest days, there was a trend for a decrease in C/Cr between dawn and dusk, while during social exposure days there was an opposite trend. Significant interactions were found between social exposure vs rest (P = 0.0005) and social exposure vs sessions (P = 0.002). Urine marking was more frequent in male than female dogs. The frequency of urine marking also appeared to be positively associated with C/Cr. Non-invasive monitoring of physiological markers could be a useful tool in assessing behaviour modulation following intraspecific socialization exposure. C/Cr was characterized by high individual variability and interactions with examined factors. The identification of new markers such as serotonin for assessing welfare in dogs is highly desirable.