Dietary effects on pelage emissivity in mammals: Implications for infrared thermography

Infrared thermography is becoming popular to measure animal surface temperature non-invasively. However, its application in quantitative mammal research is restricted by a paucity of pelage emissivity measurements, which are necessary to acquire accurate temperature readings. Furthermore, the factors influencing pelage emissivity remain largely unknown. We therefore examined the putative links between diet (fat content), hair length, hair diameter, and pelage emissivity in laboratory mice. Individuals maintained on high-fat diets had higher pelage emissivity values than those on standard diets, which may be due to fur being oily and/or the fact that the fur clumped together, exposing the skin underneath. Alternatively, the chemical composition of the fur of individuals on a high-fat diet may vary from those on a standard diet. We found no significant relationships between various hair metrics and emissivity. This study highlights that aspects of an animal's life history (e.g. age, sex, diet) may contribute to the emissivity of its pelage. As such, a single emissivity value may be inappropriate for use in infrared thermography across all species or individuals; other aspects of an animal's biology, which may affect emissivity, should also be considered. Best practice should involve measuring emissivity for every individual animal used in thermography studies.