Which statement about enrichment and study variability is most accurate?

• A. Enrichment has no impact on variability.
• B. Enrichment universally increases the risk of infection.
• C. Enrichment increases stress and variability.
• D. Enrichment can reduce stress and variability by supporting species-typical behaviors.

Answer: (D)

Enrichment helps animals express their natural behaviors, which lowers stress and makes their responses more stable across individuals. When animals can forage, hide, nest, explore, or socialize appropriately, their physiological and behavioral stress signals decrease. That reduction in chronic stress leads to more consistent baseline measurements and less variability in how different animals react to experimental procedures, improving data reliability.

The other statements misrepresent the impact of enrichment. Enrichment does influence variability, it does not universally increase infection risk, and it does not generally raise stress levels. Proper, species-appropriate enrichment tends to reduce stress and the resulting variability, rather than increase them.