Feature

Just a Rat in a Gilded Cage

Could changes in standard laboratory caging conditions make for a better life for the lab rat?

Emily Patterson-Kane, Dr Maree Hunt and Dr David Harper

The general public has come to expect that all captive animals can and should be kept in conditions that allow them to have a good quality of life. We have seen pictures of animals undergoing painful procedures or living in restrictive environments, and have decided that this is no longer acceptable. However, turning this expectation into reality is sometimes more difficult than it appears.

We cannot simply provide the animal with things that we find pleasing on the assumption that the animal will also enjoy them. Every species has evolved behaviours suited to their own lifestyle, and preferences for their own kind of environment. Before designing new conditions for an animal we need to find some way to "consult" with the animal and determine what its needs are.

We recently took the the first step in the process of analysing and improving the cages of laboratory rats kept in the School of Psychology at Victoria University of Wellington. These animals are not normally subject to invasive or stressful procedures, but they are kept in cages that may be too small and barren. This study was done to establish whether the cages needed to be improved.

Assessing Animal Welfare

There are two basic ways to assess the welfare of an animal. The most common one involves putting in place a possible improvement, and measuring the animals reaction. The animal may come to behave more like a "normal" wild animal. However, laboratory rats have been selectively bred for thousands of generations to not act like wild rats in many key ways, so they are likely to have very different needs to their wild counterparts. They have to live in an environment that includes unnatural aspects, such as being handled and examined by humans. Thus it does not make sense to use the wild rat as a "template" for domestic rat behaviour.

One way around this would be to measure the rats' preference for different conditions rather than their behaviour in them. Unfortunately preference measures only tell us which condition is better. They will not say whether either condition is "bad" or "good". Before using a procedure like this we should ascertain whether the existing conditions compromise the animals welfare.

If we know that the animal is suffering very poor welfare, then we know to make a large change and expect a dramatic improvement. If we find the animal's welfare is good, then we need to think again about what made us worry about its welfare in the first place. Were we trying to improve the rat's life, or just making them looking more pleasing to our eyes?

The second approach would be to assess the current conditions and only try to improve them if the evidence suggests that they are having a bad effect on the animal. There are many experiments which have kept rats either in small simple (deprived) cages, or large complex (enriched) cages, and then measured aspects of their brain and behaviour. These experiments have established the kinds of conditions are demonstrably bad for rats, and some which are demonstrably good. The current study used the same conditions and procedures to compare our standard conditions with these "good" and "bad" conditions that we already know so much about. This involved keeping separate groups of rats in the different types of cages for thirty days and then comparing the groups using standardised tests of their behaviour.

Open Spaces and Mazes

The most commonly used behavioural tests of the effects of deprived and enriched environments are the open field and the Hebb-William's maze, and we used these to compare standard conditions in New Zealand with deprived and enriched conditions.

The open field is essentially a large empty box. The experimenter places rats individually in the box and uses their activity levels as a measure of the aversiveness of the situation. Rats in an aversive situation "freeze" and are inactive. This behaviour probably functions as a way to avoid detection by predators that are sensitive to movement as a visual cue. Rats that have come from spatially restricted environments are more likely to freeze in the open field. The degree of inactivity is an index of the impact that the smallness of the home cage had on the rat's fearfulness. It is assumed that more fearful animals experience poorer welfare as changes to the environment and experimental manipulations will be more stressful to them.

Environmental enrichment studies use the Hebb-William's maze to detect cognitive deficits in rats from deprived environments. Rats from deprived environments have no contact with toys, barriers or other rats. It is possible that they do not develop normal learning and memory skills, as the environment would not provide opportunities to develop these. The Hebb-Williams maze consists of 12 patterns of barriers with food (chocolate) at the end. The rats ran through each pattern eight times and their maze "score" is the total number of "dead ends" entered during all 96 trials.

We compared the open field and Hebb-William's maze scores of rats kept in standard housing (standard rats) against those of rats kept in deprived and enriched caging (deprived and enriched rats). The deprived and enriched housing were based on average conditions provided in the previous theoretical studies. The enriched environment saw 12 rats in a cage which included nest boxes and objects that were changed daily; the deprived condition was a bare aluminium cube containing one rat, . The deprived condition has been previously shown to produce significant deficits on both tasks and is therefore probably unacceptable for long-term housing.

It remained to be seen whether the standard conditions produced the same deficits in rats that the deprived conditions did. If the rats had no such deficits then there may be no need to change the basic requirements for laboratory rats as New Zealand standard conditions are sufficient. If the standard rats do show the same deficits, the need for some form of enrichment is indicated.

The enriched condition, although beneficial, is too time- and space-consuming to maintain on a long-term basis, and makes handling the rats very difficult. The task would be to produce an environment that produces the same beneficial effects more efficiently. This experiment also included a quasi-enriched condition that was an attempt to achieve this, with a set-up made from two cages containing toys, pillars and four rates.

Which is Better?

There was a significant effect of caging condition on the first two minutes of activity in the open field. The rats from the smaller cages were less active. There was an approximately equal increase in activity across the groups from deprived, standard, quasi-enriched to enriched. So although the standard rats' results were closer to the deprived, the still relatively small quasi-enriched cage produced rats with scores more like enriched rats.

There was also a significant effect of caging on Hebb-William's maze scores. In this case deprived and standard rats performed equally poorly. The quasi-enriched cage again produced results mid-way between the standard and enriched rats.

Overall, the results from the standard rats resembled those of deprived rats more than enriched rats, particularly in the maze results. This finding is a concern for a behavioural laboratory that routinely investigates complex behaviours such as memory and learning. Such research could be confounded by the effect of the relatively barren cage environment on the rat's ability to perform.

However, it is unclear exactly what behaviour the Hebb-William's maze measures. It is normally referred to as problem-solving ability (or "intelligence" in earlier studies). Future studies will endeavour to discover the specific nature of the deficit. The open field is a fairly straight forward test of a fear response in a standard environment. It is not clear what aspect of the open field is aversive, but it may be the large size of the space compared to the home cage. Previous studies that used small or enclosed fields did not find that the enriched rats were more active. Regardless of the specific nature of the deficits, the current results are enough to justify further work with an aim to improve the standard environment

It is not yet clear exactly which aspects of the housing environment are most responsible for the differences between the groups. Various studies have tried to separate the effects of space, social group and objects. However results have been mixed, probably because of the range of actual conditions used. For example, space might be the most important factor for improving very small cages, but for larger cages manipulatable objects may have greater effect.

None of the previous studies of this sort used conditions like the current "standard" caging. Future studies will use preference and demand procedures to try and determine what kind of intervention -- space, other rats, objects -- is most attractive to rats from standard environments. Early indications are that no one aspect is greatly preferred, although the complete enrichment is.

Although the only likely threat to the welfare of rats in behavioural laboratories is their restrictive caging, this study indicates that the housing conditions are a significant threat and immediate steps should be taken to reduce or eliminate it. Laboratory cages provide food, water and warmth, but even rats seem to require more from life than this...their cages may not be so "gilded" after-all.

Dr David Harper works in the Psychology Department at Victoria University, Wellington
Dr Maree Hunt works in the Psychology Department at Victoria University, Wellington
Emily Patterson-Kane is studying in the Psychology Department at Victoria University.