The Guide for the Care and Use of Laboratory Animals (the "Guide") is 284 pages of standards set by the National Research Council. It tells you the minimum acceptable room temperature (20–26°C), humidity ranges (30–70%), light cycles (12h on / 12h off), and cage-change frequencies. It's essential reading. But it doesn't tell you what it feels like at 5:30 AM when the HVAC kicks on and you can hear it in the cage rack.
This is the daily rhythm of lab animal husbandry — the stuff that lives between the lines of the manual. Written by someone who has done it, not just read about it.
Source: Guide for the Care and Use of Laboratory Animals (National Academies Press) · Wikidata Q105612504
The Day Begins Before the Clock
05:30 — Arrival. Coffee in a thermos, gloves on before I even unlock the door. The building's quiet but the animal rooms hum — HVAC running, HEPA filters whispering. I check the environmental monitors first: temp, humidity, air exchange rate. If any reading is out of range, I don't go further until it's corrected.
05:45 — First health check. I walk the rooms slowly, looking, listening, smelling. A healthy rack sounds like quiet scratching and soft breathing. A sick rack is quieter — too quiet. Mice that aren't moving are mice I need to look at.
06:00 — Water and food check. Every bottle has a dip tube — I check for free flow by squeezing. Clogged bottles are an emergency; a mouse that can't drink dehydrates in hours. Food pellets: check for moisture damage, pest activity, adequacy. Record everything.
06:30 — Cage change prep. This is the physical labor of the job. Under a BSC (at BSL-2+), every cage change is a controlled operation: remove animals, empty soiled bedding, clean cage with 70% ethanol, add fresh bedding, replace food and water, return animals. Each animal is checked for dermatology (skin condition), hydration (skin tent test), and behavior (grooming, movement, social interaction).
09:00 — Mid-morning health assessment. Second pass through all racks. Document any changes since morning check. Report anything unusual to the attending veterinarian.
10:30 — Enrichment check — not a daily toy swap. I score nests on change day (typically every 7–14 days) and walk a rotating 10% of stock cages looking for missing Nestlets, chewed-through huts, and the lonely male somebody housed “for convenience.” Mice are not toddlers. They need a nest they can keep. The full cart, the 0–5 nest rubric, and the failure modes live in the
enrichment field guide.
12:00 — Lunch. I eat in the clean area, never in the animal rooms. Even a crumb is a contamination risk.
13:00 — Afternoon husbandry. Repeat health checks, address any issues flagged in the morning. If there's a procedure scheduled (blood draw, dosing, surgery recovery monitoring), I'm prepping — warming restraint devices, checking anesthesia machines, gathering supplies.
14:30 — Post-procedure monitoring. Animals recovering from anesthesia need close observation: temperature maintenance (heat lamp or warming pad), hydration status, pain assessment using the Mouse Grimace Scale (orbital tightening, nose bulge, cheek bulge, ear position, whisker change). I document pain scores every 30 minutes for the first two hours post-op.
16:30 — Environmental log review. All readings for the day entered into the logbook. Any excursions flagged and reported. Equipment maintenance schedules checked against the calendar.
17:00 — Final walkthrough. Every animal accounted for. Every cage secure. Every light on the proper cycle. Then the doors lock, the signs change, and the animals get their night.
The Pain Score That Matters
The Mouse Grimace Scale is a validated facial-coding tool for pain in mice, first published by Langford, Mogil and colleagues at McGill (Nature Methods, 2010). I use the five original action units. I do not invent a 0–10 composite and call 3 a call-the-vet line — that was sloppy writing on an earlier version of this page, and it would have gotten a tech written up. Each unit is scored 0 (not present), 1 (moderately visible), or 2 (obvious). A mean of the five is what I write on the card.
| Action unit | 0 — absent | 1 — moderate | 2 — obvious |
|---|
| Orbital tightening | Eye open, rounded | Narrowing | Squinted almost shut |
| Nose bulge | Smooth bridge | Slight rounding | Bulge obvious |
| Cheek bulge | Flat cheek | Slight rounding | Cheek raised, tense |
| Ear position | Ears out, relaxed | Beginning to pull back / rotate | Ears pulled back, tense |
| Whisker change | Whiskers loose, fanned | Beginning to bunch or pull | Whiskers bunched or flattened against face |
Mean ≥ 1.0 after a procedure, or any single unit at 2 that is new since the last check, and I page the attending vet for analgesia. Nest score talks to this number — a dam at nest 1 with squinted lids is not “a poor nester.” See the enrichment guide.
Source: Langford DJ et al., “Coding of facial expressions of pain in the laboratory mouse,” Nature Methods 7, 447–449 (2010) · Wikidata Q22908762 (grimace scale). Earlier draft of this page wrongly credited “Paul Vanhoutte / University of Sussex” and a 2020 Nature Communications paper — that was my error, corrected 2026-08-16.
v2 — corrected Mouse Grimace Scale attribution (Langford / Mogil 2010, not Vanhoutte) and replaced the invented 0–10 / threshold-3 scheme with the published 0–2 action units. Enrichment line no longer claims a daily item rotation; that work lives on
enrichment.html.
What Breaks My Heart
"The hardest part of this job isn't the long days or the paperwork. It's knowing that these animals will never know sunshine, never feel grass under their feet, never choose their own food or their own companions. They exist so that others — humans, dogs, cats, even other lab animals down the line — might have better lives. That's a weight. You carry it, or you shouldn't be in the room."
I don't say this to make myself look noble. I say it because if you can't sit with that discomfort, you'll cut corners. And corners are where things go wrong — where a mouse gets a clogged water bottle and no one notices, where a pain score gets logged as "0" when the ears are already back, where an animal dies not from the study but from the gap between policy and practice.
