RQA GLP Committee
Routinely, in large animal studies, there should be separation of control and treated animals. There may occasionally be only a small number of animals on test and therefore, if welfare requirements mean that the animals should be group housed then there maybe justification for this, depending on dose route. It might also be possible to house a non-study animal with the study animals for welfare reasons. This should be a discussion between your QA and your NACWO and the decision documented as to the agreed solution.
Be careful with this, it is preferable to avoid this situation if at all possible.