Yes: Mice Live Fast, So Records Must Keep Up
Keep the log, because a fancy mouse packs its life into a short span and can move from apparently well to clearly unwell in days, which makes a weekly record one of the highest-value habits in mouse keeping. Weigh each mouse weekly on a fine-reading scale, in a small container it knows, and write the figure down per individual, even in a group where the mice look similar at a glance. A mouse quietly losing condition while cage mates hold steady is a classic early finding that only individual records reveal, since group feeding can mask one animal eating less when competition or illness separates it from the food.
That per-mouse discipline is the real answer to the question: a shared note saying the mice seem fine is not a log, while dated weights for each animal are.
Notes That Matter at Mouse Scale
Beside each weight, record appetite, energy in the evening, coat condition, and breathing. Mice breathe quickly, and any audible clicking, wheezing, sneezing fits, or laboured effort should be written down with the date it started, because respiratory history is among the first things a vet asks about in this species and owners otherwise remember it vaguely. During gentle handling, feel carefully along the body and note any lump you find, its location in plain words, and whether it changes at the next check; record observations without trying to judge them yourself, since a dated size comparison is useful to a vet whatever the cause turns out to be.
Note social changes too, such as a mouse sleeping alone that usually piles with the group, being excluded from the nest, or grooming a cage mate excessively, because in group mice behaviour is health data. Log food, bedding, and group changes alongside, so a dip can be read in context.
Thresholds for a Prompt Vet Visit
A mouse's speed of life compresses your response times as well. A confirmed falling weight trend, breathing that becomes audible or effortful, a lump that grows between checks, persistent scratching with coat damage, or a mouse that is hunched, cold, and quiet should all prompt a vet visit promptly rather than another week of notes, because mice have minimal reserves. Take the log to the appointment; in a ten-minute consultation, your dated weights and breathing notes may be the most diagnostic material in the room.
Keep vet findings in the same record, including any instruction to monitor a lump or recheck weight, placed beside the entries that will carry out that instruction. For a group, keep each mouse's page distinct within the one file, with a photograph or written description at the top of each page so records are never attributed to the wrong animal.
A Two-Minute Weekly Habit
Weigh during the evening clean or handling session you already have, keep the scale with the enclosure supplies, and record the unremarkable weeks as faithfully as the worrying ones. Anyone helping with your mice should be able to read the current page and know each mouse's normal weight, breathing, and behaviour, because at mouse speed a helper's observation may be the one that matters. Review monthly for drift, and retire pages respectfully when a mouse dies, keeping its record with the group's file as part of their shared history.
A notebook by the cage cannot attend the vet visit across town. Through KinsLe, Pet Passport keeps every fancy mouse's individual weight log, breathing and coat notes, and vet records together in one portable place, so each small animal's history is complete wherever it is treated.