Laboratory rats are commonly used to study energy homeostasis. To accurately record food intake or energy expenditure it is necessary to house rats individually, which can be stressful for social animals. Environmental enrichment may reduce stress and improve welfare in laboratory rodents. However, the effect of environmental enrichment on food intake and thus experimental outcome in rats is unknown. We aimed to determine the effect of environmental enrichment on food intake, body weight, behaviour and faecal and plasma stress hormones in male Wistar rats.
Singly housed rats were given either no environmental enrichment, chew sticks, a plastic tube, or both chew sticks and a tube (n=68 per group). These forms of enrichment are commonly used in rodent husbandry and have been shown to promote species-specific behaviour.
No differences in body weight or food intake were seen over a seven-day period. Importantly, the re-feeding response following a 24-h fast was unaffected by environmental enrichment. Rearing, a behaviour associated with stress, was significantly reduced in all enriched groups compared to controls. No differences in faecal corticosterone were noted between groups throughout the study. However, there was a significant increase in faecal Immunoglobulin A and a trend towards a reduction in plasma corticosterone in animals housed with both forms of enrichment compared to controls at the termination of the study, suggesting enrichment may reduce hypothalamopituitaryadrenal axis activity in singly housed rats.
In summary, environmental enrichment does not influence body weight and food intake in singly housed male Wistar rats and may therefore be used to refine the living conditions of animals used in the study of energy homeostasis without compromising experimental outcome.