Increasing focus on issues of research reproducibility affords us the opportunity to review some of the key issues related in vivo research. First, we set out some key definitions, to guide the reader through the rest of the paper. Next we consider issues of epistemology, of how animal experiments lead to changes in our understanding of biomedicine and, potentially, to the development of new therapeutics. Here we consider the meaning of statistical significance; the importance of understanding whether findings have general truth; and the advances in knowledge which can result from 'failed' replication. Then, we consider weaknesses in the design, conduct and reporting of experiments, and review evidence for this from systematic reviews and from experimental studies addressing these issues. We consider the impact that these weaknesses have on the development of new treatments for human disease, and reflect on the response to these issues from the biomedical research community. Finally, we consider strategies for improvement including increased use of brief, pre-registered study protocols; pre-registration, open publication and open data; and the central importance of education in improving research performance.
