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Johns Hopkins Bloomberg School of Public HealthCAAT

Animal Welfare Enhancement Awards - 2004 Recipients

Evaluation of Two Non-Contact Infrared Thermometers for Determining Changes in Body Temperature in Mice
Colette Wheler
 University of Saskatchewan

Hypothermia can be an important indicator of a deteriorating condition in an animal, especially in studies involving viral and bacterial infections. However, methods to accurately measure body temperature in mice are limited. A high performance non-contact thermometer used in the food industry (Raytek Raynger MX2) has been used to measure changes in temperature by aiming the beam at the sternum of mice (Laboratory Animals 2003, Volume 37 Number 2 pages 126 - 131). This thermometer measures surface body temperature, as opposed to core body temperature, but seems capable of tracking changes in body temperature in a very non-invasive manner.

This study is being undertaken to further investigate the use of the Raytek Raynger MX2 thermometer, and compare it to the less expensive Minitemp FS thermometer. The specific objectives of this study are outlined below, followed by preliminary results of each objective:

  1. Using a Raytek Raynger MX2 non-contact thermometer, to measure surface body temperature at 4 different sites in adult female C57/BL6 and CD1 mice to test for repeatability of reading.

    Preliminary Results:

    Difficulty was encountered in being able to find 4 different sites (spots) that could accurately be measured with this thermometer. This was partly due to initially not understanding the concept of distance to spot ratio. The measured spot depends on the distance between the object being measured, and the infrared thermometer. With the MX2 Close Focus, to measure a spot size of 0.24" (6 mm - about the diameter of the hub of a needle), the thermometer needs to be held 12 inches (30 cm) away from the mouse. It was impractical and unwieldy to hold the thermometer a foot away from the mouse. The solution was to measure a spot size of 0.75" (19 mm - about the diameter of a penny), at a distance of 4" (10 cm). However, the small size of the mouse limited the locations (spots) of this diameter that could be measured. The number of sites was reduced to 2: directly between the hind legs, and over the sternum. The readings have been taken, and statistical analysis is pending, to test for repeatability of reading at these two locations. It was easier to take a reading between the hind legs, and this seemed less stressful on the mouse.

  2. Using the MiniTemp MT4 non-contact thermometer, to measure surface body temperature at 4 different sites in adult C57BL6 and CD1 mice to test for repeatability of reading.

    Preliminary Results:

    The same difficulties were experienced with the MiniTemp thermometer. With the MiniTemp, the smallest spot size capable of being measured is 1" (2.5 cm — about the diameter of a quarter), at a distance of 4" (10cm). Again, the number of sites was reduced to 2: directly between the hind legs, and over the sternum. The MiniTemp is smaller than the MX2, and easier to aim and use. The readings have been taken, and statistical analysis is pending, to test for repeatability of reading at these two locations.

  3. Using the data from Objectives 1 and 2, to compare the Raytek Raynger MX2 model with the less expensive MiniTemp MT4 model for repeatability of reading

    Preliminary Results:

    Side by side readings have been taken using the MX2 and the MiniTemp. Statistical analysis is pending.

  4. To compare change in body temperature using radiotelemetry with change in body temperature using the Raytek Raynger MX2 non-contact thermometer during an actual experimental study

    Preliminary Results:

    One of our researchers contacted us prior to doing a study that involved using change in temperatures to determine endpoints. This researcher uses subcutaneously implanted microchips to monitor temperature. Both the MX2 and the MiniTemp were compared to the microchips, however, due to personnel changes during the study, and temperatures not changing much, the information collected was not very useful. The plan is to try to monitor changes in body temperature of mice under anesthesia, using both the MX2 and the MiniTemp, compared to a fine rectal probe. This study has yet to be done.

  5. Ultimately, to discover whether the use of a non-contact food thermometer may provide a non-invasive method for accurately determining change in body temperature of mice, in order to facilitate observation of humane endpoints in experimental studies.

    Hopefully, once all studies are complete and the statistical analysis has been done, some practical recommendations can be made on the use of non-contact thermometers to measure changes in body temperature in mice.