Selected Contribution: Ambient temperature for experiments in rats: a new method for determining the zone of thermal neutrality

TLDR

The thermoneutral zone (TNZ) of an animal varies with the physical environment, contrary to the common belief that it is constant, and existing methods to determine it are complex and limited. The study aims to develop a rapid, broadly applicable method to assess whether experimental conditions are thermoneutral for a given animal. The method defines TNZ by three criteria—large skin temperature fluctuations, skin temperature near the median of its range, and a strong negative correlation with core temperature—and validates it using thermocouple thermometry and liquid crystal thermography across five rat strains at 13 ambient temperatures. The technique identified a TNZ of 29.5–30.5 °C for Wistar, BDIX, Long‑Evans, and Zucker lean rats, and 28.0–29.0 °C for Zucker fatty rats, demonstrating that skin thermometry or thermography is a simple, inexpensive, definition‑based method to classify experimental conditions as neutral, sub‑neutral, or supra‑neutral.

Abstract

There is a misbelief that the same animal has the same thermoneutral zone (TNZ) in different experimental setups. In reality, TNZ strongly depends on the physical environment and varies widely across setups. Current methods for determining TNZ require elaborate equipment and can be applied only to a limited set of experimental conditions. A new, broadly applicable approach that rapidly determines whether given conditions are neutral for a given animal is needed. Consistent with the definition of TNZ [the range of ambient temperature (T a ) at which body core temperature (T c ) regulation is achieved only by control of sensible heat loss], we propose three criteria of thermoneutrality: 1) the presence of high-magnitude fluctuations in skin temperature (T sk ) of body parts serving as specialized heat exchangers with the environment (e.g., rat tail), 2) the closeness of T sk to the median of its operational range, and 3) a strong negative correlation between T sk and T c . Thermocouple thermometry and liquid crystal thermography were performed in five rat strains at 13 T a . Under the conditions tested (no bedding or filter tops, no group thermoregulation), the T a range of 29.5–30.5°C satisfied all three TNZ criteria in Wistar, BDIX, Long-Evans, and Zucker lean rats; Zucker fatty rats had a slightly lower TNZ (28.0–29.0°C). Skin thermometry or thermography is a definition-based, simple, and inexpensive technique to determine whether experimental or housing conditions are neutral, subneutral, or supraneutral for a given animal.