Worldwide trends in the use of animals in research: the contribution of genetically-modified animal models

The Three Rs -- Reduction, Replacement and Refinement -- which were first proposed in 1959 by Russell and Burch, have become widely accepted principles in the governance of humane animal research. However, there is substantial variation in the ways in which different countries document the numbers and types of research animals used, making it difficult to determine how effectively the Three Rs are being implemented. Here, we provide the first data illustrating worldwide trends in animal use for research purposes. To document global trends in animal use, we sampled 2691 articles from 24 countries, published between 1983 and 2007, in four scientific journals. We show that the percentage of articles reporting animal use has risen in the past 15 years. The rising popularity of genetic modification methods has contributed to this trend: reported genetically-modified animal use has more than doubled since 1997. We also show that mice are the most commonly-used species for genetic modification, and that, even in 2007, relatively inefficient random integration methods were still widely used to achieve genetic modification. These results illustrate shortcomings in the effort to implement the Three Rs in animal research.