Affective and behavioural interactions between human handlers and laboratory rats

In laboratory settings, human-rat interactions are necessary and frequent, yet the impact of different handlers on the behaviour of the animal is underexplored. This study examined how human behavioural responses - confidence, experience, and physiological arousal - relate to affective indicators in rats, specifically ultrasonic vocalisations (USVs) and behavioural responses. 50-kHz USVs, associated with positive affect, were significantly higher post-handling compared to during handling, but no aversive 22-kHz calls were observed. Correlation analyses found that rat behavioural distress scores were positively associated with handler behavioural distress scores and negatively associated with handler's confidence. Heart rate increased during handling, particularly among moderately experienced handlers (1-5 years), but was not associated with rats' behavioural distress measures. Experience was positively correlated with confidence but not directly associated to rat behaviour or handlers heart rate. These findings suggest that observable human behaviour, rather than physiological arousal or years of experience, can potentially influence rats' emotional responses with the potential implications for animal welfare and scientific outcomes.