Use of Infrared Termography (IRT) in laboratory animals environment: preliminary note

Framing the work in view of the principle of the 3Rs (Replace, Reduce, Refine) the objective of this experimental test is to assess what benefits are obtainable by the application of infrared imaging technique (IRT) to analyze the status of laboratory animal welfare. This technique still needs to be validated for the study of thermoregulation in rodents used for experimental purposes. The rodents’ breeding environment should be constantly monitored and the individually ventilated cages (IVC) offers several advantages. The purpose of the trial was to evaluate the environmental differences between open cages and IVCs. The evaluation was performed with aid of a TVS 500 EX camera. Twelve female nude mice, of 6 weeks of age, housed within the enclosure of Institute “Mario Negri” in Milan were randomly divided into 4 cages, 2 of which IVCs and 2 open cages. The animals were fed ad libitum with a standard diet and had free access to water. The room temperature was set at 22 ± 2 °C with a relativehumidity of 52% and 18 - 20 air changes per hour. The air changes in a conventional cage are 5 - 10 per hour. In IVC, controlled air changes were 75 per hour, preserving room humidity and CO2 percentage. Measurements were collected weekly from the 9th to the 12th week of age. The cages were placed under a vertical laminar flow hood and, after removing the cover, animals were video-recorded for 4 minutes. Values obtained from the interscapular area, where the Brown Adipose Tissue (BAT) is located, and the base of the tail were recorded. As for the BAT and tail measurements, the most remarkable difference between cages was recorded at the first week of observation, namely the 9th week of life of the mice. This could be due to the fact that inside the IVC the temperature was two degrees higher than that recorded in the room: the higher temperature detected in the BAT of mice housed in open cages could reflect an higher activation of the tissue in response to a lower environmental temperature. In this case we observed a reduction of the temperature of the tail due to vasoconstriction of the vessels. In conclusion, the present research demonstrates the possibility of using IRT to evaluate the skin temperature and BAT of nude mice in different environmental conditions.