NIH Wants to Count Every Mouse — and Publish the Number. NOT-OD-27-001 Is the Most Consequential Animal Welfare Notice in a Decade.

The Office of Laboratory Animal Welfare issued a Request for Information on September 25 that will not generate a single headline in the general press and will reorganize animal care administration at every institution holding a Public Health Service Animal Welfare Assurance. NOT-OD-27-001 asks a question that sounds procedural — is annual reporting of live vertebrate animal numbers feasible? — and whose answer determines whether roughly 90 percent of American research animals move from uncounted to publicly tabulated.

Comments are due December 21, 2026, submitted electronically through the NIH RFI portal. Responses are voluntary and may be submitted anonymously. OLAW specifically invites input from both domestic and foreign institutions with approved Animal Welfare Assurances, which is a meaningfully broader respondent pool than most NIH policy RFIs address.

The Gap This Closes

American laboratory animal oversight runs on two parallel tracks that cover different animals and demand different reporting.

The Animal Welfare Act, administered by USDA's Animal and Plant Health Inspection Service, covers dogs, cats, nonhuman primates, rabbits, guinea pigs, hamsters, and other warm-blooded species — but statutorily excludes purpose-bred rats and mice, along with birds bred for research. AWA-covered institutions file an annual report with animal counts broken out by USDA pain and distress categories: Column B for animals held but not used in research, Column C for procedures involving no pain or distress, Column D for pain or distress relieved by anesthetics or analgesics, and Column E for pain or distress where relief was withheld because it would have compromised the scientific objective. Those reports are public.

The PHS Policy on Humane Care and Use of Laboratory Animals, administered by OLAW, covers all live vertebrates — mice, rats, zebrafish, Xenopus frogs, birds, every domesticated and nondomesticated vertebrate species used in PHS-funded work. Field investigations observing nondomesticated species under natural conditions are excluded. But the PHS Annual Report to OLAW does not currently require animal numbers at all. Institutions report average daily inventory by species in the Domestic Animal Welfare Assurance, which is a facility-capacity document, not a usage census.

The practical result is that the United States has precise, public, pain-categorized counts for the small minority of research animals covered by the AWA and no systematic federal count of the mice, rats, and fish that constitute the overwhelming majority. Estimates of total U.S. research animal use vary by an order of magnitude depending on whose methodology you accept, because the underlying number does not exist.

NOT-OD-27-001 proposes to close that gap by extending AWA-style reporting — animal numbers plus USDA pain and distress categories as defined in the Animal Welfare Act Regulations — to PHS-covered species the AWA does not reach. OLAW states that annual reports by institutions would be made publicly available online.

The Eight Questions, and What They Are Really Testing

The RFI asks institutions to address:

1. Current methods for compiling institutional animal numbers, including the software used and whether pain and distress categories are captured.
2. Whether animals are already tracked internally or for external oversight bodies, and what data those systems hold.
3. A feasibility assessment, including which specific aspects of the proposed reporting would be infeasible.
4. A realistic implementation timeline.
5. Required institutional resources — budget, staffing, systems.
6. Anticipated benefits and drawbacks.
7. Additional work and burden, direct and indirect.
8. Any further opinions or suggestions.

Read as a set, these questions are not neutral. Questions 1 and 2 establish what institutions already have, which sets the baseline against which any burden claim in questions 5 and 7 will be judged. An institution that answers question 1 by describing a modern animal census platform with per-protocol tracking has substantially weakened its own ability to argue in question 7 that aggregation is prohibitively expensive. This is standard regulatory RFI construction, and institutions should answer it with that structure in mind — not by understating capability, but by being precise about the gap between what their systems record and what the proposed report would demand.

Because that gap is where the real burden lives, and it is not where most people assume.

The Burden Is Pain Categorization, Not Counting

Most institutions with an IACUC and a modern vivarium can produce a mouse count. Per-cage and per-protocol census data already exists because it drives per-diem billing. Aggregating it annually is a reporting exercise.

Assigning USDA pain and distress categories to every mouse, rat, zebrafish, and frog is a different undertaking entirely. The categories are not properties of an animal; they are properties of what was done to the animal, and the assignment requires professional judgment about whether a procedure caused more than momentary pain and whether anesthetics or analgesics were withheld for scientific reasons. For AWA-covered species, institutions have built that judgment into protocol review and annual reconciliation over decades, for populations typically numbering in the hundreds or low thousands.

Extending it to a rodent and aquatic population that at a large research university runs to hundreds of thousands of animals annually, across many hundreds of active protocols, is a categorical change in scale. Genetically modified mouse colonies raise a question the RFI does not resolve: in a breeding colony where a fraction of pups carry a phenotype causing pain or distress, and most animals are maintained solely to produce experimental subjects, which animals land in Column B and which in Column D? Zebrafish facilities face the same question with populations in the tens of thousands per tank system. These are the specifics worth putting into a question 3 response, because "infeasible" as a bare assertion will not move OLAW and a worked example of an ambiguous colony will.

The Public Posting Is the Policy

The burden conversation will dominate institutional comment letters, and it is the less important half of the notice.

OLAW's statement that annual reports would be made publicly available online is the provision with downstream consequences. AWA annual reports are already public and already used — by advocacy organizations tracking Column E usage, by journalists, by state legislators drafting research animal bills, and increasingly in litigation. Extending public reporting to rodents and fish means that for the first time, an institution's total research animal usage and its distribution across pain categories becomes a published, comparable, year-over-year number.

That changes institutional risk in ways no additional data-entry hours capture. A university whose Column E rodent count rises because a single pain research program expanded will have that increase visible and attributable. Comparisons across peer institutions become trivial, and the comparison will not be adjusted for research portfolio. Institutions that comment only on administrative burden and ignore the publication provision will have conceded the part of the notice that actually matters to them.

There is also a defensible counter-case worth making, which is that reliable public numbers are the precondition for institutions to demonstrate reduction over time. Right now, an institution that cuts rodent use 30 percent by adopting organoid and organ-on-chip methods has no federal mechanism to show it. The counting infrastructure that creates reputational exposure also creates the only evidence base for claiming progress.

Why This Notice Is Arriving Now

NOT-OD-27-001 does not appear in isolation. NIH has spent 2026 building the scientific and physical infrastructure for reducing animal use: the Complement-ARIE program committed $150 million to human-based New Approach Methodologies across seven technology development centers, a data hub, and a validation network. In late September the agency announced $88 million in biomedical research facilities construction tied to NAMs capacity, a Bio Genesis Autonomous Human Biology Laboratory in the NIH Clinical Center, and the NCATS Qu-SAFE prize competition putting $7.1 million behind quantum sensing for in vitro toxicity models.

Every one of those investments is a replacement technology. None of them can be evaluated without a denominator. You cannot show that organoids reduced animal use if you never knew how many animals were used. Reading NOT-OD-27-001 as an animal welfare measure understates it; it is also the measurement layer for a research reduction agenda that NIH has already funded at nine figures.

That framing has a practical implication for comment strategy. Institutions arguing for a long implementation runway are more persuasive when they tie the timeline to NAMs adoption milestones than when they cite staffing alone.

What to Do Before December 21

Run the gap analysis now, not in December. Pull what your animal census system can already produce: counts by species, by protocol, by fiscal year. Then attempt a pain and distress categorization for one month of rodent data. The hours that exercise consumes is the number that belongs in your question 5 and question 7 responses, and it is far more credible than an estimate.

Decide the colony question and state your answer. Breeding colonies, genetically modified lines with painful phenotypes, and aquatic facilities are the three places the proposal is genuinely ambiguous. Institutions that propose a workable categorization rule in their comment have a real chance of seeing it adopted. Institutions that merely flag the ambiguity will get whatever rule emerges from someone else's comment.

Address the publication provision explicitly. Ask for what you actually need — portfolio context published alongside counts, a defined correction process, a lag before posting, or aggregated rather than per-institution release in the first reporting years. None of that will be offered if nobody requests it.

Coordinate, but do not only coordinate. Association comment letters from AAALAC-accredited institutions, AAU, and COGR will carry weight on policy design. Individual institutional letters carry weight on feasibility, because they contain the operational specifics association letters cannot. Both are worth filing.

Comments close December 21, 2026. Responses may be anonymous, which lowers the cost of candor about what your systems actually cannot do — and candor on that point is the single most useful thing an institution can contribute to this record.