Over 100 Million Mice per Year in US labs? No One Knows

No One Knows.

January 2021, I published my article estimating how many mice and rats per year we use in United States labs every year. The reality: No One Knows. For two reasons:

1. The patchwork of US regulations and accreditations means that no one is actually reporting mouse and rat use in a publicly transparent way, given that these animals are excluded from the Animal Welfare Act definition of “animals.”
2. No one has a consistent definition of “used.”  Every mouse that becomes a data point in a paper or a regulatory test has parents, siblings, and colony-mates who do not get that far. If you include breeders and culled animals, you find a larger number “used” than if you only count those who become data points in published papers. 

My approach relied on getting annual reports to the accreditation agency, AAALAC. They get annual reports from labs they accredit, but never release such confidential info. Some labs were willing to give me their info as reported to AAALAC. Some gave me the info via their state’s Public Records act.  For the 16 labs whose data I received, mostly well-funded universities, I then compared annual rat/mouse use to annual Animal Welfare Act “animal” use on annual reports on the USDA website.  When I put those together, I found that at those 16 large campuses whose data I got, Rats/Mice were more about 99.3% of the mammals. Extrapolating from an annual report in 2018 of over 780,000 AWA “animals,” I estimated over 110 million mice and rats, which is a good three times what others – research advocacy groups and animal advocacy groups – have been saying. 

I did this project because I’d pretty much guessed pretty much this number in my 2004 book, What Animals Want, and always figured someone would do some actual data-gathering to check on this. Almost no one did, and the one group that did used European stats to get at US numbers, and I do believe they ended up under-estimating US mice and rats in the process. So, I did it myself. 

As David Grimm found writing about my estimate in Science, there was some pushback. Some pretty vehement pushback, as these things go. 

Here’s my review of the criticisms of my paper, and some response

First, my own criticisms of my project (which I do discuss in my paper): 

1. This is hampered by having no standard definition of “used,” even for labs that do report to NIH or to AAALAC. My guess — but remember: no one knows — if you include breeders and culled animals (including the ones at commercial breeding labs) I imagine there’s a 10-fold increase compared to just counting those animals enrolled in an experiment or euthanized for their tissues. But no one knows.
2. Even if we had an agreed-upon definition of “used,” NIH and AAALAC have not given a uniform definition of “how many” or “average daily census.” At some places, especially if they count cagesto bill to grants, there’s no standard industry conversion factors for converting numbers of cages on a given day to numbers of mice on that day, and even less, for going from average daily number of cages to total annual numbers of animals used. I found a wide range of conversion factors in my project, but the truth is: no one knows.
3. When there is such an imbalance (my data found a 99.3 to 0.7 difference, though I actually think my 99.3% is on the low side), any small difference in the estimated balance of mice to larger animals is magnified. So, while 99.2% seems not far off from 99.6%, there’s a large difference between 0.8% and 0.4%   So if all you can really get are counts of the small numbers of animals reported to the USDA, that 0.4, 0.8 or other really could make a big difference in your estimated totals. 
4. The big challenge with my project: if all I can get are mouse counts from a handful of institutions, mostly from those subject to states’ sunshine laws, is that sample representative enough of all US labs in academia and industry?
5. I also only looked at one year’s data. That may be more faith than warranted in our counting and reporting systems. 

I tried to lay out my methods in enough detail that even if I’m over (or under-estimating) the project might be reproducible enough to show trends over the years. 

Others’ critiques:

Nadia Jackson at Jackson Labs thinks my university sample would not be representative, and I’m wrong to work with that assumption. She’d rather make assumptions based on commercial info from Charles River labs, which seems to be the world’s largest supplier of lab rodents. If you make certain assumptions about what percent of their revenue is mouse and rat sales, and what the average price of the mice they sell is, and an assumption that people across the country buy about three-fourths of their mice and only breed one fourth in-house AND you assume that the numbers of unsold (breeders; culled animals) at vendors selling 15 million mice per year are negligible, the total number is only about 20 million.  I do think that’s a lot of assumptions to come up with that number, and I see no reason to think her assumptions are any more valid than mine. Because as we know, with no clear windows into mouse labs, No One Knows.

Speaking of Research does not like my look over to Europe (or up to Canada or over to Australia) for the idea that the US should transparently report on numbers of animals used. Guilty as charged, but they do also critique my estimate. They point out (correctly) that my data are skewed toward large universities, or rather the subset of those that I was able to get data from (and yes: thanks to those of you who told me your mouse numbers. I promised you anonymity, and I’m honoring that, as well as to those who refused my request). True. They point out that 7 large private companies use more USDA-covered animals (e.g., hamsters, dogs, monkeys, some pigs) than the 50 largest NIH-funded universities. They don’t say how I could get at those places’ mouse and rat numbers to let me make a nation-wide extrapolation to total mouse numbers. They may be write that my sampling is not representative enough. Maybe if someone uses my methods, they can go further down the level of funding hierarchy and see if lesser-funded universities do indeed have different mouse rat ratios. That would be great. Until then, I still think I’ve got the most reproducible method.

At the National Association for Biomedical Research and Foundation for Biomedical Research, I don’t see any dispute about my estimate, just their concerns about what people would do with my estimate, which I’ll write about separately. Their estimate is that mice and rats are 95% of lab animals (notice we’re all avoiding mentioning zebra fish, where lack of transparency or standardized counting are even greater, so No One Knows if they outnumber mice. They may). That would mean that for the year I covered, there were about 15 – 16 million mice and rats.