Date of Award


Degree Type


Degree Name

Master of Science (MS)


Comparative Pathobiology

First Advisor

Brianna N. Gaskill

Second Advisor

Marguerite E. O'Haire

Committee Chair

Brianna N. Gaskill

Committee Co-Chair

Marguerite E. O'Haire

Committee Member 1

Sylvie Cloutier


Rats initially fear humans which can lead to negative affect, poor welfare, and difficult handling. Also, modeling and measuring positive affect states in rats can pose an additional challenge. Heterospecific play, or “tickling,” is a handling habituation technique that mimics rat rough-and-tumble play that is being used to study positive affect. It can also be used to reduce fear of human, improve welfare, and elicit a positive affect state. However, current studies implementing the technique in laboratory rats use a wide variety of protocols to achieve differential results. Unlike in laboratory environment, pet store rats experience high levels of novelty and potentially inconsistent human interactions which may reinforce fearful human-rat relationships. Thus, pet rats may experience benefits from tickling. Also, although anecdotal information suggests tickling may have positive effects on humans, this assertion has not yet been empirically validated. The central hypothesis for this thesis was that tickling rats would improve rat welfare and human-rat interactions.

A systematic review of empirical research using rat tickling identified 55 experiments within 32 articles. Although a wide variety of methods were used, main outcomes of tickling compared to a control condition included increased number of positive vocalizations and approach behavior, decreased anxiety and fear metrics, improved handling reactivity, and, in some cases, decreased stress hormones. There were also specific factors that could moderate outcomes from tickling including rat age, housing type, presence of bedding, and inter-individual differences. The most consistent effect found was that there are distinct inter-individual differences in rat response to tickling in that some rats consistently produce more 50-kilohertz vocalizations, a measure of positive affect, than others. Rats that produce more 50-kHz vocalizations are termed high-callers. Overall, our review showed that tickling is a promising method for improving rat welfare and investigating positive affect, but that further investigation into best practices is warranted.

To expand the current research conducted on laboratory rats into the pet store setting, we investigated the effects of tickling pet store rats on human-rat interactions, animal welfare, as well as all the people that interact with the rats. We predicted that tickled high-calling rats would show the most positive responses and that humans would be positively affected by tickling. In each replicate, rats were first randomly split into control handling and tickling groups; tickled rats were further split into two groups based on their number of vocalizations produced during 3 days of tickling for 5 minutes a day. Once the rats were allocated to their groups, trained employees tickled animals from both tickling conditions for 4 days. We assessed employees using the Animal Empathy Scale and the Positive and Negative Affect Scale. Using a survey, we asked customers which cage of rats they would purchase and which cage of rats looked happiest. Finally, we assessed new rat owners with surveys and the Lexington Attachment to Pets Scale. We assessed rats using in cage video behavior, fecal corticosterone, and an unfamiliar human approach and restraint test.

Our results showed that tickled rats were easier and faster to restrain and were less inactive than control rats. Additionally, behavioral factors such as high activity were cited as very important to selection by both in-store customers and new rat owners. Employee affect and overall animal empathy were unaffected by short-term tickling, but at the point of sale employees were slightly more positive about selling control rats. Finally, customers were more likely to identify tickled high-calling and control rats as being happier. In the unfamiliar approach tests, tickled low-calling rats showed more behaviors indicative of anxiety and fear than tickled high-calling rats.

Taken together, the results of this thesis build upon previous tickling literature by presenting an original application of tickling in pet stores as well as evaluating the technique’s effects on humans. Overall, based on the welfare benefits of tickling for rats combined with short-term minimal to positive effects for humans, we recommend using tickling as a habituation technique for pet store rats, particularly high-callers.