Housing environmental enrichment influences mouse behavior and response to experimental metabolic disorders

Housing environmental is essential for animal welfare but may also influence the metabolic and behavioral outcomes of preclinical studies. This study investigates whether two commonly used enrichment materials, Nestlets and Sizzle, modify the effects of a high-fat diet (HFD) on metabolic and behavioral phenotypes in adult male C57BL/6 J mice. A total of 128 mice were fed either a normal diet (ND) or HFD for six months and housed in enriched cages containing either Nestlets (Nest) or Sizzle nesting material ( n = 32 mice/condition). Metabolic parameters and behavioral performances were assessed at six months. Results show that HFD induced weight gain, hypercholesterolemia, fasting hyperglycemia, and impaired glucose tolerance under both enrichment conditions. However, Nest-enriched mice displayed lower cholesterol levels and differences in glycemic responses compared with Sizzle-enriched mice, suggesting that nesting material can modulate the severity of diet-induced metabolic alterations. Furthermore, environmental housing also affected behavior. Nest-enriched mice showed higher locomotor activity and reduced anxiety compared with Sizzle-enriched mice. Interestingly, HFD-induced impairment of visual recognition memory in the novel object recognition test was detected only in Nest-enriched mice. Overall, these findings demonstrate that different enrichment materials can substantially modify metabolic, emotional, motivational, and cognitive responses to HFD. These results highlight the need to carefully control and consistently maintain housing environmental conditions throughout long-term preclinical studies to improve reproducibility, interpretation of behavioral outcomes, and animal welfare.