A single mouse

From John M. Barry, The Great Influenza, page 160. In describing some of the testing on mice Barry mentions:

Male mice were and are generally not used in experiments because they sometimes attack each other; the death or injury of a single mouse for any reason can distort experimental results and ruin weeks of work.

Which makes sense. But I am surprised to come across this only now and in this place after so many hundreds if not thousands of science papers I have read over the years. It makes me wonder what, if any, bias or distortion using only female mice might have introduced into over a century of medical research from this pragmatic response to a quotidian issue. Presumably none, but you have to wonder.