Animal numbers used in animal research

To put animal use for scientific purposes into perspective, in the Netherlands, yearly, approximately 530.000 animals are being used in this context. To note, this is substantially less than the 641.000.000 animals that are killed yearly in the Netherlands for meat consumption, the 140.000.000 animals (e.g. birds) that are killed yearly in the Netherlands by pets, the tons of fishes that are captured by commercial and recreational fisheries and the unknown numbers of animals that are yearly killed as unwanted wild fauna (‘pests’). The exact numbers are published every year in “Zodoende” and the exact current approximates can be found there.

Within the TNU, in 2019 we used 2582 mice and 1023 rats. Of these 707 rats and 1921 mice had a cumulative severity of mild,  232 rats and 466 mice had a severity of moderate and  75 rats and 53 mice had a severity of severe.  Experiments with severe discomfort for the animals are rare at  TNU and only fall into that classification due to including multiple procedures that themselves do not not cause great discomfort (e.g. 2-3 surgeries for specific techniques with intervening recovery periods each procedure classified as moderate) or more stressful behavioural techniques such as foot shock (to investigate the impact of psychological trauma or stressful event on mental disease development).

Nine rats and 142 mice were part of only non-recovery experiments (no severity listed). As part of breeding procedures 1210 rats and 2724 mice were bred but not used in experiments. This is due to e.g. animals not expressing the desired gene or are the wrong gender. For example, when one wants to investigate a disease that is based on homozygote gene expression (both copies of the gene need to be affected) but breeding is based on both parents being heterozygote (having only one affected copy and one non-affected copy), there will be 25% offspring with no affected gene (these animals can be used as controls in experiments), 50 % offspring which are heterozygote (can be used for e.g. further breeding) and only 25% with the desired genotype with two affected gene copies. Therefore, not all animals that are born can be used in investigations into this specific type of disease, at the same time it is impossible to avoid having these animals when breeding for certain genotypes. However, it is important to know that animals that are bred but not used in experiments do not undergo any discomfort since they do not receive any treatments or other kinds of interventions.

In 2020 1882 mice and 848 rats. Of these 514 rats and 941 mice had a cumulative severity of mild,  228 rats and 809 mice had a severity of moderate and 98 rats and 24 mice had a severity of severe. 8 rats and 108 mice were part of only non-recovery experiments (no severity listed). As part of breeding procedures 1210 rats and 2307 mice were bred but not used in experiments.