The number of animal experiments carried out by Utrecht University and UMC Utrecht rose slightly over the past year, from 12,584 in 2024 to 13,226 in 2025. However, the number of animal experiments involving rats and mice is showing a steady downward trend. This is evident from the joint Annual Report on Animal Experiments 2025.
“After two years of a sharp decline, we are now seeing a slight increase in the number of animal experiments again,” says Pascalle van Loo, head of the Animal Welfare Body Utrecht. “The increase is mainly attributable to the use of a large number of zebrafish over the past year. As the number of animal experiments is relatively low, fluctuations in experiments involving large numbers of animals can have a greater impact on the total. This is also the case in 2025, as 2,635 zebrafish were used in experiments – 2,447 more than in 2024.”
The number of animal experiments involving mice and rats shows a steady downward trend from 15,595 to 9,011 over the period 2015–2025, the period during which the amended Animal Experiments Act has been in force. “This shows that, despite fluctuations caused by experiments involving large numbers of animals, there is an overall downward trend,” says Van Loo.
In 2025, six animal experiments were carried out on elephants. Researchers from the Faculty of Veterinary Medicine worked on developing a vaccine against a deadly herpes virus in elephants, a disease that particularly affects young animals in zoos. The efficacy of this vaccine is being tested in collaboration with various zoos in the Netherlands and across Europe. “This type of research underlines the societal and veterinary relevance of our work, and our commitment to contributing to animal health and welfare, even beyond traditional animal testing models,” says Debbie Jaarsma, Dean of the Faculty of Veterinary Medicine, in the foreword to the annual report.
Read the 2025 Annual Report on Animal ExperimentsWould you like to know more about the 2025 Annual Report on Animal Experiments? Please contact Pascalle van Loo, Head of the Animal Welfare Body: 06 2330 6783.
