Earlier this month, the European Commission published its first ever count of all laboratory animals used in research and testing (see Nature http://doi.org/dmvh; 2020). The report, which includes data from 2015 to 2017, indicates that the number of experimental animals in the European Union remains fairly stable, at around 9.5 million per year. In addition, many animals (14 million in 2017, for example) are used simply to create and maintain genetically altered lines or are killed because they are the wrong genotype, sex or age. By including these ‘surplus’ animals, Europe is taking a lead in transparent reporting.

This figure might seem high, but the need for experimental animals to meet defined requirements means that some animals will inevitably be surplus. Nevertheless, these numbers can be reduced by using alternatives to animal experimentation. For every two animals not used in testing, three supporting animals could be saved. Researchers can help by planning their experiments carefully, using online tools such as preregistration (B. Bert et al. PLoS Biol. 17, e3000463; 2019).

Refinement strategies should pay more attention to the welfare of surplus animals because there tend to be fewer restrictions on their living conditions than for animals used directly for research (L. Lewejohann et al. Lab. Anim. http://doi.org/dmvj; 2020).