LAUSR

Abstract Rats find initial interactions with humans frightening, which can lead to negative affect, and poor welfare. A handling technique called “tickling”, which mimics rat rough-and-tumble play, can be used to reduce these negative effects. When tickled, rats produce 50 kilohertz (kHz) ultrasonic vocalizations (USV) indicative of positive affect. During tickling, some rats consistently vocalize more (high-callers) and react more positively to novelty and stress than rats that utter fewer vocalizations (low-callers). Rats in pet stores can experience high levels of environmental novelty, as well as infrequent and inconsistent human interaction, which may reinforce a fearful human-rat relationship. We hypothesized that tickling pet store rats improves human-rat interactions and animal welfare, particularly for tickled high-callers, as compared to non-tickled controls or tickled low-callers. Across 2 replicates, 36 female rats were sampled with 6 minimally handled controls and 12 tickled rats per replicate. Tickled rats were split into two groups, high-callers (most USVs) and low-callers (least USVs), based on tickling for 3 days (5 min/rat/day). Handling treatments were applied by store employees for 4 additional days. During these 4 days, feces were collected to assess fecal corticosterone levels and continuous video recordings were made to quantify play behavior, activity level, and location. Finally, rats were assessed with an unfamiliar human approach (60 s), manual restraint (30 s) and second human approach test (60 s). Results showed in an unfamiliar human approach and restraint test, tickled rats required fewer restraint attempts and shorter time to restrain than controls (p  In conclusion, short-term tickling of pet store rats improves ease of restraint with an unfamiliar handler. In comparison to low-calling rats, high-calling rats show less fear toward unfamiliar humans. Tickled rats had higher arousal levels based on fecal corticosterone, which may relate to their anticipation of interaction with humans. Overall, our results suggest that tickling pet store rats may improve some human-rat interactions, especially for tickled high-calling rats.