Submitted to: Journal of the American Association for Laboratory Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/22/2017
Publication Date: 5/1/2017
Citation: Johnson, J.S., Taylor, D., Green, A.R., Gaskill, B.N. 2017. The effects of nesting material on energy homeostasis in BALB/cAnNCrl, C57BL/6NCrl, and Crl:CD1(ICR) laboratory mice housed at 20°C. Journal of the American Association for Laboratory Animal Science. 56(3):254-259.

Interpretive Summary: Although current laboratory animal housing and temperature recommendations have been well-established, numerous recent studies indicate that the recommended temperature for mice (20 to 26°C) may be below their lower critical temperature. As a result of this discrepancy between standard laboratory housing practices and the preferred thermoneutral zone of mice (26 to 34°C), cold stress can occur. Because mild cold stress in mice can alter their physiological state, housing mice in an environment below thermoneutrality could lead to errors in extrapolating physiological, pharmacological, and toxicological findings from experimental rodent models to humans. Therefore, re-evaluating and refining laboratory animal management practices and housing protocols is a crucial step in improving animal wellbeing and increasing the repeatability and validity of scientific data. To reduce the effect of mild cold stress on laboratory animals, nesting material can be provided that allows for the formation of microenvironments, which can improve thermoregulation and stabilize metabolic rate by reducing the reliance on increasing metabolic heat production to maintain euthermia. In the present study, our objective was to determine the optimal amount of nesting material (0, 6, or 12 g Enviro-Dri) required to limit energy loss as heat and improve energy balance in three common strains of mice housed at current recommended temperatures during the daytime when mice are inactive. We hypothesized that increasing the amount of available nesting material would decrease metabolic heat production and improve energy balance in mice. We have now confirmed that during the daytime when mice are inactive, providing greater amounts of nesting material can improve energy balance and reduce reliance on stored energy substrates, likely due to a reduction in cold stress-induced thermogenesis. Furthermore, the enhanced energy balance and metabolic stability associated with increased provision of nesting material has obvious implications towards reducing stress in lab animals and improving research quality when using mice as an animal model.

Technical Abstract: Objective: A discrepancy exists between the preferred ambient temperature range for mice (26 to 32°C) and the current recommendations (20 to 26°C) that can result in mild hypothermia. As a consequence, animal welfare may be reduced and physiological state can be altered, which can impact research integrity in studies using mouse models. Previous research indicates that providing nesting material can alleviate the negative impact of cold stress on thermal comfort in mice; therefore, the study objective was to determine the optimal amount of nesting material (0, 6, or 12 g Enviro-Dri) required to limit energy loss as heat and improve energy balance in three common strains of mice housed at current recommended temperatures during the daytime when mice are inactive. Methods: Thirty-six groups (5mice/group) of BALB/cAnNCrl (BALB/C), C57BL/6NCrl (BLK6), and Crl:CD1(ICR) (CD1) mice, equally distributed between type of mice and sex, were group housed and provided either 0g, 6g, or 12g of Enviro-Dri nesting material. After a 3d acclimation period, body weight (BW) was determined daily at 0800h, and feed intake (FI), and total heat production (HP) were evaluated from 0800h to 2000h on 4 consecutive d and used to calculate energy balance and the respiratory quotient (RQ). Results: Regardless of sex or strain, providing 12 g of nesting material increased the BW of mice. No nesting material differences in FI or HP were observed. Providing 12 g of nesting material improved energy balance during times of inactivity and the increase in positive energy balance was corroborated by an increase in RQ compared to mice provided 0g or 6 g of nesting material. Conclusions: Providing greater amounts of nesting material can improve energy balance and reduce reliance on stored energy substrates during times of inactivity. This is likely due to a reduction in cold stress-induced thermogenesis, which may have implications towards reducing lab animal stress, stabilizing metabolic rate, and improving research quality when using mice as research models.