How are rats weighed? - briefly
Rats are placed in a ventilated weighing chamber or a pre‑weighed holder on an analytical balance designed for gram‑scale measurements. The displayed mass is corrected by subtracting the tare weight of the container.
How are rats weighed? - in detail
Accurate measurement of a laboratory rat’s mass is essential for dosing, growth monitoring, and physiological studies. The process begins with animal acclimation: rats are placed in a quiet room for at least five minutes to reduce stress‑induced weight fluctuations. Handling is performed with gentle scruffing or by allowing the animal to step onto a platform voluntarily, minimizing movement that could affect the reading.
Two primary instruments are employed:
- Analytical balance (precision scale) – capacity 0.1 g, readability 0.001 g. The rat is placed in a pre‑weighed, breathable container (e.g., a small plastic cage or a paper cup with ventilation holes). The container’s tare weight is recorded, then the combined weight is measured. The animal’s mass is obtained by subtracting the container’s mass.
- Platform balance (digital rodent scale) – capacity up to 5 kg, readability 0.01 g. The scale surface is calibrated, and the animal is gently positioned directly on the platform. Some models include a built‑in enclosure to prevent escape and reduce handling time.
When using an analytical balance, the following steps ensure reliability:
- Calibrate the balance with certified weights before each session.
- Verify the tare of the empty container.
- Record the combined weight within three seconds of placement to limit movement artifacts.
- Repeat the measurement three times; calculate the mean value.
For platform scales, protocol includes:
- Zero the instrument with the empty platform.
- Place the rat centrally; allow it to settle for no more than two seconds.
- Record the displayed weight; repeat twice for consistency.
- If the rat attempts to jump, gently restrain using a soft cloth to avoid injury.
Environmental factors that influence precision:
- Temperature – maintain ambient temperature between 20 °C and 24 °C to prevent thermal expansion of the scale components.
- Air currents – operate the balance inside a draft‑free enclosure or under a laminar flow hood.
- Humidity – keep relative humidity below 60 % to avoid moisture affecting electronic sensors.
Data handling: enter each measurement into a laboratory information management system (LIMS) with timestamp, animal identifier, and instrument model. Apply the average of repeated readings as the final weight, noting any deviations exceeding 5 % of the mean for further investigation.
By adhering to calibrated equipment, standardized handling, and controlled environmental conditions, researchers obtain reproducible mass data essential for accurate experimental outcomes.