Huddling and nest building do not completely ameliorate the cold stress of typical housing in mice

Huddling and nest building are two methods of behavioral thermoregulation commonly utilized by mice under cold stress. Lab mice are typically housed at an ambient temperature (T a ) of 20°C, approximately 10°C below their thermoneutral zone of 30°C. We tested the hypothesis that the thermoregulatory benefits of huddling and nest building would lower heart rate (HR), blood pressure (BP) and metabolic rate (MR) of mice housed at 20°C to levels typical of mice housed at 30°C. C57Bl/6J mice were implanted with EKG/BP/core body temperature (T b ) telemeters, housed in metabolic cages and, using a repeated‐measures crossover design, exposed to one of four conditions: 1) singly housed at 20°C, 2) group housed at 20°C, 3) singly housed with nesting material at 20°C, 4) singly housed at 30°C. Mice singly housed at 20°C had a 24 hour HR of 607 ± 20 bpm, mean BP of 98 ± 4 mm Hg, MR of 1.5 ± 0.1 ml O 2 /min and food consumption of 16.6 ± 5.0 kcal/day. The nesting only condition significantly changed only HR (Δ‐51 bpm). Group housing changed both HR and food consumption (Δ‐62 bpm and Δ‐2.6 kcal/day). Singly housed mice at 30°C had changes in all measured parameters (Δ‐239 bpm; Δ‐5 mm Hg; Δ‐0.6 ml O 2 /min; Δ‐5.8 kcal/day). No significant difference was found in T b among the groups. These findings indicate that huddling and nest building lessen but do not completely ameliorate cold stress at 20°C.