The use of animals in experimental research has soared at leading US laboratories in recent years, finds research published online in the Journal of Medical Ethics.
This is despite growing public opposition to animal experimentation, mounting evidence that animal studies often do not faithfully translate to people, and the development of new research technologies that supplant animal use.
The data contradict industry claims of reduced animal use and are at odds with government policies designed to curb and replace the use of animals in experiments, say the researchers.
The US is the world's largest user of animals in experiments, and government data show declines in the use of cats, dogs, primates, rabbits, hamsters and other larger mammals.
But the exclusion of the species most commonly used in laboratory research - mice, rats, birds bred for experimentation, and all cold-blooded animals - from federal regulations has resulted in an absence of published data on how many of these animals are used in experiments.
To fill this gap, researchers at People for the Ethical Treatment of Animals (PETA) used Freedom of Information requests to obtain and analyse previously unpublished data collected by the US National Institutes of Health (NIH) on the use of all vertebrate species at the top 25 institutions in receipt of its grants.
The analysis showed that use of animals in laboratory research at these facilities rose by just under 73 per cent between 1997 and 2012.
This was largely driven by increases in the use of mice while the use of other species remained mostly unchanged. Unregulated species made up almost all (98.8 %) of the animals used at these labs.
This is the first time data on the prevalence and trends in use of these species in the US has been published, and the pattern mirrors international reports of increases in the use of mice for genetic modification.
Possible explanations for these trends include personal and legal biases towards certain animal species, say the researchers. But the figures highlight a need for greater efforts to curb the use of animals in scientific research and more transparency in reporting on whether these are succeeding, they add.
A linked viewpoint acknowledges the ongoing tensions between scientists and animal rights advocates, but suggests that people on both sides of the divide do want to better understand one another.
It recommends that institutional policies be updated to better inform the public about the use of animals in scientific research, as well as opening up dialogue between a broad base of players to replace the current often poorly informed and emotionally charged debate.