Sylvie Cloutier, Ph.D., and Ruth C. Newberry, Ph.D., present playful handling as social enrichment for laboratory rats

When animals are used in research,there is seldom, if ever, a focus on affectionate or playful handling. However, based on what has already been proven about rats and their response to positive caregiver contact, we at the Washington State University Center for the Study for Animal Well-Being set out to explore management and husbandry factors in the laboratory that improve the welfare of the rats being studied and the outcome of the research.

Our team investigated how the provision of playful social contact between rats and humans that mimicks playful social contact between rats minimizes the adverse effects of individual housing in response to handling, standard procedures and behavioral tests used in biomedical research.

Rats are highly social mammals. For this reason, communal housing is recommended for rats used in biomedical research. However, they sometimes have to be housed individually, due to research constraints or medical issues. Individual housing deprives rats of social contact, which can increase anxiety, fearfulness and aggression. There is therefore a need to find social stimuli that could improve their welfare. Since humans are integral members of the social environment of laboratory animals, increased positive interaction with the animal care staff has been recommended by the National Research Council as social enrichment for individually-housed animals. However, the types of social interaction that would be most effective are not specified and, more importantly, not well researched.

Human contact with rats is likely to be most effective when it mimics the rat's own behavior. If so, tickling rats in a manner that simulates the bodily contact that occurs during rat social play may be a useful and practical method for enrichment. Playful tickling can be done by making rapid finger movements across the nape (where rats usually solicit play), followed by vigorous tickling of the belly. When rats are tickled, they emit ultrasonic vocalizations (USVs) at a specific frequency (50-kHz) which can be detected with an ultrasonic microphone (i.e. a bat detector) and sound recording software. These 50-kHz USVs are the same as those emitted during social play, suggesting that when playing and being tickled, these rat chirps, like human laughter, reflect a positive affective state.

If ticking is an enjoyable experience for rats, tickled rats should greet their caretakers with enthusiastic USVs and playful solicitations, rather than withdrawing in fear and struggling to escape when handled. Tickling by caretakers could be especially useful in a research setting if tickled rats become less fearful and more receptive toward humans in general, enabling them to adapt faster to new people and situations. It would also be useful if it provides an adequate substitute for social housing for individually-housed rats.

Socially-housed rats are kept in groups of two or more, depending on space availability, cost constraints and study requirements. Social housing for rats therefore means housing in pairs. Pair-housed rats, however, have been reported to show intermediate responses between individually-housed rats and rats housed in groups of three or more in some behavior tests. Furthermore, when given the choice, rats spend more time in groups of three or more than in pairs or alone. Therefore, pairing might not be a suitable "social housing" standard against which to compare the responses of individually-housed rats. A better understanding of the effects of housing rats in pairs versus trios would be useful. In fact, if individually-housed rats exhibit a desire to be tickled by people, and rats housed in trios turn out to be rather indifferent to human tickles, it would be interesting to find out whether pair-housed rats respond more like individually- or triple-housed rats. Even if tickling has no immediate benefit for rats housed in pairs and trios, it would be useful to know if tickling these rats when they are young would have any benefit in the future if they later had to spend some time in individual housing.

We conducted an experiment to investigate these possibilities and compared the responses of 72 male Sprague-Dawley rats that, for the first three weeks after weaning, were either tickled daily for two minutes by their caretakers or kept with only the minimal handling involved in transferring them into a clean cage once a week (the control condition). Rats in each of these situations were housed in groups of one, two or three. In the fourth week, we measured the rats' attraction to unfamiliar humans in a novel environment. All of the rats were then placed in individual housing with minimal handling for the next three weeks and tested again in the eighth week. The effectiveness of tickling as social enrichment was evaluated by measuring the emission of ultrasonic vocalizations. Ease of handling was assessed during weekly cage cleaning using a handling score (0 = no struggling to 4 = energetic struggling).

We found that tickled rats emitted more 50-kHz calls in anticipation of being handled than rats used to only minimal handling (Figure 1).

Further, they also struggled less than the control rats when handled during cage cleaning, a difference that was statistically significant over the eight weeks of the experiment.

These effects of tickling applied to all rats, whether housed individually, in pairs or in trios. The effects also persisted after discontinuation of the tickling program, when all rats were moved into individual housing. Although tickling increased USVs and reduced struggling when handled by a familiar caretaker, it did not result in increased attraction towards the hand of an unfamiliar person.

Our results indicate that daily tickling for two minutes over a three-week period improved the relationship between rats and their caretakers. Tickling was equally beneficial for rats regardless of whether they were housed individually or in groups of two or three rats, and the benefits persisted throughout a four-week break from tickling. Although tickling did not increase attraction to unfamiliar people, it was our subjective impression that tickled rats were more comfortable in the presence of familiar people who had never tickled them than rats that had not been through the tickling program. We conclude that daily tickling is a good source of social enrichment for individually-housed rats, and that this type of playful interaction with people is also beneficial for socially-housed rats.

About the Authors

Sylvie Cloutier, Ph.D., is a research assistant professor at Washington State University Center for the Study of Animal Well-Being. She has 19 years of research experience in animal behavior and welfare working with domestic chickens, pigs, degus and laboratory rats.

Ruth C. Newberry, Ph.D., is an associate professor in the Center for the Study of Animal Well-Being at Washington State University, with appointments in the Department of Animal Sciences and the Department of Veterinary and Comparative Anatomy, Pharmacology and Physiology. Her research is focused on environmental enrichment and social behavior.

This research project was made possible through a Refinement Award from the Animal Welfare Institute.