Submitted on July 4, 2006
Accepted on October 30, 2006
APPARATUS FOR MEASURING RAT BODY VOLUME:
A METHODOLOGICAL PROPOSITION
Rodrigo Hohl1*, Renato Buscariolli2, Denise Vaz Macedo1, and Rene Brenzikofer3
1 Biochemistry, UNICAMP, Campinas, São Paulo, Brazil
2 Biochemistry, Universidade Estadual de Campinas - UNICAMP, Campinas, São Paulo, Brazil
3 Biomechanics, UNICAMP, Campinas, São Paulo, Brazil
* To whom correspondence should be addressed. E-mail: magvx{at}hotmail.com.
We propose a communicating vessels system to measure body volume in live rats through water level detection by hydrostatic weighing. The reproducibility, accuracy, linearity and reliability of this apparatus were evaluated in two tests using either previously weighed water or six aluminum cylinders of known volume after proper system calibration. The applicability of this apparatus to measure live animals (Wistar rats) was tested in a transversal experiment with five rats, anesthetized and non-anesthetized. We took 18 measurements of the volume under each condition (anesthetized and non-anesthetized) totaling 90 measurements. The addition of water volumes (50--700ml) produced a regression equation with a slope of 1.0006±0.0017, intercept of 0.75±0.81 (R2=0.99999 and SEE=0.58ml) and a bias of about 1ml. The differences between cylinders of known volumes and volumes calculated by the system were lower than 0.4ml. Mean volume errors were found between 0.01% and 0.07%. Regarding the live models, the mean±SD difference between the volumes obtained for anesthetized and non-anesthetized rats was 0.31ml±2.34ml (n=90). These data showed that animal movement does not interfere with the volume measured by the apparatus proposed, and neither anesthesia nor fur shaving is needed for this procedure. Nevertheless, some effort should be taken to eliminate air bubbles trapped in the apparatus or the fur. The proposed apparatus for measuring rat body volume (AMV) is cheap and may be useful for a range of scientific purposes.
