Diets fed to laboratory animals have become standardised, so that that they meet the nutritional needs of the animal, and are also produced to a fixed “recipe” so that variation is minimised. Diets must be stored correctly to ensure that nutrient loss before use is minimised. Similarly, bedding of a standardised material should be provided and stored carefully. Both diet and bedding could be attractive to wild rodents and birds, and storage facilities must be designed to avoid the possibility of exposure of this type since this could result in the introduction of disease agents.
Although the diet and bedding provided to laboratory animals may meet their nutritional needs, it can sometimes be necessary to feed supplements, for example as part of positive reinforcement training, or to encourage animals to eat following surgery or other procedures. Use of such supplements is often of considerable benefit, but they should be standardised when possible, and details recorded in the study protocol. The feeding of “treats” on an ad-hoc basis should be discouraged unless first agreed with all concerned with the management of each study.
Similarly, use of additional items of bedding, such as nesting material, should be standardised, and this can easily be achieved on a facility-wide basis, and modified as needed for individual studies. The choice of additional items to enrich an animal’s environment will vary depending upon the species, but for rodents will often include nesting materials, “chew sticks” and a refuge or shelter. Adding complexity to the environment, and allowing animals to use all of the volume of the cage by including resting areas and shelves can also benefit their welfare. Environmental enrichment must be selected carefully, so that it has the desired effect of enhancing the animals’ welfare, and improving their biological functioning. It should increase the frequency and diversity of positive natural behaviours and decrease the incidence of abnormal behaviours such as stereotypies. It should also maximise their utilisation of their environment and increase their ability to cope with the stressors they are exposed to.
Environmental enrichment strategies for all species usually include socialisation which can either be direct, where this is both appropriate for the species and the study design, or by means of visual or olfactory contact when direct contact is not possible or desirable. The animals’ accommodation should provide an interesting and stimulating environment, feeding may be adapted to enable foraging behaviour (Fig. 1), and diets may include different textures and tastes. Manipulative objects, or objects allowing natural behaviour such as gnawing (e.g. chew sticks) can be included and extra bedding can be provided for burrowing behaviour or nest building.