How can a rat’s body temperature be determined? - briefly
A rectal thermometer or an implanted telemetry transmitter yields precise core temperature measurements in rodents. Infrared cameras can estimate surface temperature, but they are less accurate for determining internal body heat.
How can a rat’s body temperature be determined? - in detail
Accurate assessment of a rodent’s core temperature requires direct or indirect measurement techniques that are validated for small mammals.
Rectal probe insertion remains the most widely used method. A lubricated, calibrated thermistor or digital thermometer (0.5 mm diameter) is inserted 2–3 cm into the anal canal, allowing rapid equilibration within 10–15 seconds. Readings are recorded to the nearest 0.1 °C. This approach yields high precision (±0.2 °C) but can cause stress; brief handling and habituation reduce variability.
Infrared thermography provides a non‑contact alternative. A high‑resolution infrared camera captures surface temperature of the dorsal or ventral thorax. Calibration against a known blackbody source and ambient temperature correction are essential. Surface measurements correlate with core values after applying empirically derived conversion factors (typically a 1–2 °C offset). This technique permits repeated assessments without restraint, though accuracy depends on fur density and environmental conditions.
Implanted telemetry devices deliver continuous core temperature data. A miniature telemetry transmitter, surgically placed in the peritoneal cavity or subcutaneously near the scapula, records temperature at preset intervals (e.g., every 5 minutes). Data are transmitted wirelessly to a receiver and logged for analysis. Advantages include real‑time monitoring in freely moving animals and elimination of handling artifacts. Limitations involve surgical implantation, potential tissue reaction, and device cost.
Auricular thermometry employs a small probe placed in the ear canal, exploiting the proximity of the tympanic membrane to the carotid artery. After gentle insertion, the probe stabilizes within 5 seconds. This method offers moderate accuracy (±0.3 °C) and reduced invasiveness compared with rectal probing, but ear wax and canal size variability can affect reliability.
Subcutaneous temperature‑sensitive microchips, similar to RFID tags, can be implanted under the skin. A handheld scanner reads the chip’s temperature reading without animal restraint. Accuracy is lower (±0.5 °C) and reflects peripheral rather than core temperature, making it suitable for screening rather than precise physiological studies.
Selection of a technique should consider experimental objectives, required temporal resolution, animal welfare, and equipment availability. For single, high‑precision measurements, rectal thermometry is preferred. For longitudinal studies with minimal disturbance, telemetry implants provide the most comprehensive dataset. Infrared imaging serves well in behavioral experiments where handling is contraindicated, provided environmental factors are tightly controlled.