The variability of organ weight background data in rats.

The variability of organ weight data in a series of 5 control groups of Sprague-Dawley rats was studied. Differences in body weight and organ weight data were detected between the studies. Attempts to reduce the variability of organ weights by using analysis of covariance or organ to brain weight ratios were only partially successful. Factors which may influence animals under controlled conditions and result in variability between studies are discussed. It is concluded that caution is needed when considering the use of organ weight background data as a means of comparison. The findings are in agreement with other fields of study in toxicological testing, and emphasize the importance of using a concurrent control for the purpose of comparison of data.