Body Weight Endpoint after infection - Weight loss (20%) compared with the initial weight or the highest (Sep/22/2008 )

Hello, I need to do a mouse infection experiment. The endpoint we use is 20% weight loss. I was just wondering if the 20% is related to the initial body weight before the infection or to the highest body weight during the experimental period.
The mice we use are 4-6 weeks old and the initial body weight is normally 16-18g. After a week, they can normally grow to 18-20 g without infection... If you know the answer, could you leave me with a reference as well?
Thank you.

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Hmmmm, what about using the average weight of your negative control mice, and making the cutoff 20% less than that??

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In our institution, a 20% weight loss is considered severe enough to require removal of the mouse from the study (i.e euthanasia). In fact, in our protocols, this is one of our "criteria for early removal" which are used to identify animals that are experiencing a level of pain and/or distress that require removal from the study. Thus, this has to be determined on a mouse-by-mouse basis; i.e. a loss of 20% of the mouse's original body weight at the start of the study.

Good luck,
SK

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