Abou-Ismail, U. A. 2011. Are the effects of enrichment due to the presence of multiple items or a particular item in the cages of laboratory rat? Applied Animal Behaviour Science 134(1-2), 72-82.

Although the effects of environmental enrichment on laboratory rodents have been extensively described, it is not yet known whether these effects were simply due to the presence of multiple items in the cage or due solely to the presence of a particular item. This experiment was therefore carried out to investigate whether the long-term effects of enriching cages of laboratory rats are due to the presence of multiple physical structures or due simply to the presence of a particular structure in the cage. In a two-replicate study, 96 newly weaned male Wistar rats were housed in groups of four in either retreat cages (RC), ladder cages (LC), crawling ball cages (CBC), nylabone cages (NC), wooden block cages (WBC) or multiple items cages (MIC) for five weeks. Behaviour was sampled in both the light and dark phase of the light/dark cycle every week. Measures of body weight and weight gain were collected over the five-week housing period, and organ weights were recorded post-mortem. MIC rats displayed higher levels of indicators of good welfare such as sleep and enrichment-directed behaviour, and weight of spleen and thymus gland, and lower levels of indicators of poor welfare such as aggression and awake non-active behaviour, compared to rats in the other treatments. MIC rats also spent a longer time in the open part of the cage and contacting enrichment items. It therefore appears that increasing the diversity of enrichment by the addition of multiple physical structures to cages of laboratory rats may have the potential to improve their welfare not only by increasing the complexity of the environment, but also by promoting species-specific behaviours and providing the animals with opportunities to exert some control over their environment.