Assessment of discomfort in gallstone-bearing mice: a practical example of the problems encountered in an attempt to recognize discomfort in laboratory animals.

In order to obtain practical experience on the recognition, assessment and evaluation of discomfort in laboratory animals, the degree of discomfort was studied in gallstone-free and gallstone-bearing mice. Out of nine parameters to which scores were assigned per individual mouse, only the response to palpation of the right hypochondrium was found to score significantly higher in gallstone-bearing mice. That is, the incidence of squeaking and the magnitude of muscular contractions were significantly higher in these animals compared with the gallstone-free mice. The stance of the gallstone-bearing mice also tended to be abnormal, although the difference between gallstone-free and gallstone-bearing animals did not reach statistical significance. Although this study does not prove unequivocally that the induction of gallstones per se causes discomfort or pain in mice, we tentatively conclude that it does. We feel that this should be taken into account in any projected work in which gallstone induction in animals may occur. There was considerable between-assessor variation in the assignment of scores to the variables used to assess discomfort, including the response to palpation. It is concluded that the selection of parameters and the experience and/or attitude of the assessor are critically important when the magnitude of discomfort, if any, is assessed in experimental animals.