Colour of laboratory animal cage influences mice – and experiments

Up until now, colour has not played a role in the keeping of mice, in spite of the fact that in recent years a great deal of attention has been focused on the increase in the quality of life of laboratory mice. Standard cages of tanks for laboratory animals are not designed so much in the animals' best interests as they are to make their handling easier for humans. Laboratory cages for rodents are usually small and contain nothing more than food, water, a uniform substrate and perhaps some fellow cage inhabitants. The practise of keeping animals in such minimalistic environments can change their biology and behaviour in a fundamental way, as had already been demonstrated in previous studies. Since then, efforts have been made to improve the living conditions of laboratory animals for the more subtle studies, at any rate. This involves primarily measures targeting the cage layout, for example by focusing attention on shelter and light, a more interesting substrate and cage shape. One aspect has been nearly overlooked entirely – the colour of the dwelling itself, or in the event the walls are transparent, the colour of the background – an aspect that is usually coincidental.

At the same tine, in spite of all of the human-oriented research being performed on laboratory mice, there is actually very little known about the animals' eyesight. Nonetheless, their ability to see colour is presumably similar to this capacity in humans. The researchers assumed that they had a preference for cages in certain colours. This concept is already well-known with respect to a wide variety of other animals, from turkeys to macaques. And, using man as a behavioural model for the laboratory mouse for a change instead of vice versa, it has also been demonstrated that the colour of the surroundings can influence a person's emotional state and ability to perform tasks.

More than seventy mice (Mus musculus) were provided with dwellings which had been painted red, black, green or white. Five weeks later, one-third of these were individually placed into a specially designed set-up which offered them the opportunity to choose between pens in each of these different colours. Each mouse demonstrated an extremely decisive preference. On the whole, this preference was not related in any way to the colour of the mouse's own dwelling. Most of the mice expressed a preference for a white dwelling with red being the least popular of the colours.

The other mice provided even more information. They were put to the mort "animal-friendly" test in this case. The colour of their cage appeared to have a significant influence on their body weight and food consumption.

The colour of their cage appeared to have a significant influence on their body weight and food consumption. The effect on their behaviour in a standardized test maze was also considerable. The mice from the red dwellings remained primarily motionless in dead-end branches of the cages, behaviour which points to a high level of agitation and fear.

According to the researchers, the avoidance of the red cages and their low voluntary occupancy indicates an avoidance of those environmental conditions which evoke a negative mental state. They emphasise that the colour of the dwelling can have a long-term effect on the performance of mice, even when the test situations are placed elsewhere. Mice under stress are not the healthy individuals which they are supposed to be representing in most experiments, such as those measuring the effects of medication. One could therefore say that there is simple yet effective work still to be done on their welfare as well as their usefulness as a laboratory animal.

By: Frans van der Helm / previously published in the

NRC Handelsdagblad, 24 January 2004

Sources: PETS International (www.Petsinfo.com)