Determining an Efficient and Effective Rat Tickling Dosage

Megan R. LaFollette, Dr. Marguerite E. O’Haire, Dr. Sylvie Cloutier, and Dr. Brianna N. Gaskill

Laboratory rats may experience distress during handling, which can negatively impact their welfare. Rat tickling, a handling technique that mimics aspects of rat rough-and-tumble play, has been found to induce positive affect based on production of 50-kHz ultrasonic vocalizations (USVs). However, current protocols for rat tickling are time-intensive, making its practical implementation difficult. Our objective was to identify a time-efficient and effective dosage of rat tickling. We hypothesized that affect (i.e., emotional state) and handling can be improved by small, daily doses of tickling within a five-day workweek. The study was funded through an AWI Refinement Grant.

Seventy-two rats (both male and female) of the Long-Evans strain, housed in same-sex pairs, were sampled. Each cage was randomly assigned a tickling duration (15, 30, or 60 seconds per rat) and frequency (1, 3, or 5 days). After the final day of tickling, rats were tested for ease of, and reaction to, handling via a saline injection following a tickling session for their assigned duration. On test day, we measured USVs, home cage behavior (60 minutes before and after testing), approach behavior (30 seconds before and after testing), and fecal corticosterone (a noninvasive method for determining stress hormone levels). Periods before and after testing measured anticipatory and reactionary responses, respectively. Behaviors included play, activity, location, and indicators of fear or anxiety such as rearing and contact with the hand.

Results showed that, regardless of tickling duration, rats tickled for three or five days produced a higher rate of 50-kHz USVs before and during tickling, and played more and were less inactive in their cage for the hour before tickling and injection compared to rats only tickled for one day. Approach behavior, injection duration, and fecal corticosterone were unaffected by either tickling duration or frequency. There were few differences in outcomes between a tickling frequency of three or five days.

In conclusion, we found that tickling duration did not alter any measures and that a three-day tickling frequency was more efficient and effective than a one-day frequency but similar to a five-day frequency, based on increased 50-kHz USVs (a measure of positive affect) and positive anticipatory behavior, including play. Therefore, we conclude that a time-efficient and effective rat tickling dosage is 15 seconds for three days before any potentially aversive procedures are applied. Overall, our results suggest that minimal rat tickling can be effective at habituating rats to handling and, thus, preparing them for research procedures.

Dr. Brianna Gaskill is an assistant professor of animal science at Purdue University who focuses on welfare assessment of laboratory animals. Megan R. LaFollette is a PhD student in Gaskill’s lab. Dr. Marguerite E. O’Haire is an associate professor of human-animal interaction at Purdue. Dr. Sylvie Cloutier is a research scientist with the Canadian Council on Animal Care.

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