Does environmental enrichment affect food intake and body weight in singly housed male Wistar rats?

Kylie Beale, Angela Kerton, Kirsty Smith. Imperial College, London, United Kingdom.

The World Health Organisation estimates that by 2015 over 700 million adults worldwide will be obese. Due to the huge economic and social burden of obesity, gaining a greater understanding of the pathways controlling energy balance is essential to aid the development of new treatments for this condition. Wistar rats are a well characterised animal model for studying obesity. In order to accurately record food intake or energy expenditure it is necessary to house rats individually, which can be stressful for normally social animals. Environmental enrichment, defined as the use of objects to improve the quality of life of a caged animal, can reduce the levels of stress hormones in singly housed animals. However, when studying energy balance it is unclear the effect environmental enrichment has on food intake and thus experimental outcome. The aim of this current work was therefore to determine the effect of environmental enrichment on food intake, body weight, the response to fasting and behaviour in male Wistar rats. Male Wistar rats were singly housed and randomly assigned into one of four groups (n= 6-8 per group). The control group received no environmental enrichment in their home cage. The second group were given two wooden chew sticks. Rats in the third group were given a black plastic tube and the fourth group received both chew sticks and a tube. After a five day acclimatisation period, food intake and body weight were measured daily for seven days. Behaviour was monitored in the early dark phase for one hour. The animals’ response to a 24 hour fast was determined and plasma levels of the stress hormones ACTH and corticosterone were also measured. No differences in body weight or food intake were seen over a seven day period. The re-feeding response following a 24-hour fast was unaffected. Rearing, a behaviour often associated with stress, was significantly reduced in all enriched groups compared to controls. When behaviours were grouped, the control group displayed significantly more ‘active’ behaviours than the two groups with tubing. Furthermore, plasma corticosterone was reduced in both groups with tubing compared to controls. In conclusion, environmental enrichment does not influence body weight and food intake in singly housed male Wistar rats. However, differences in behaviour were observed which may influence food intake and body weight over a longer period of time than measured in this current study. Therefore, whilst the introduction of environmental enrichment to singly housed rats may improve welfare, further work is required before it can become an established part of our feeding protocols.