Start with an identity card for each mouse
A colony record fails at its first step if you cannot say which mouse a number belongs to, so identity comes before any weighing. Give each mouse a name and back it up with the markings that actually distinguish her: a photo taken from above in good light, a note of coat colour and pattern, and any permanent quirk such as a nicked ear or an unusually pale tail. Fancy mice from the same litter can look near-identical at a glance, and two agouti sisters may only differ in one white toe. Write those tiny differences down while you can still hold each girl and check, because a weight log that mixes up two similar mice is worse than no log at all — it hides the very changes you are keeping records to catch.
Weigh each mouse the same way every time
Consistency is what turns a column of numbers into a health record. Use the same small cup or tub on the same kitchen scale, tare it with the cup empty, and weigh each mouse at the same point in her day — before the evening feed works well, when stomachs are in a comparable state. Once a week is enough for healthy adults; a mouse you are already watching can be weighed twice a week. Note the figure in grams beside her name, never as a colony total. Adult female mice are light animals, so a change of only a few grams is meaningful: a steady drift downward across two or three weigh-ins matters far more than one low reading after a busy night of running. If a mouse will not sit still, let her settle inside the cup with the lid loosely on rather than chasing a bouncing number.
Log feeding per mouse, not per cage
A shared bowl tells you what the colony was offered, not what each mouse ate. Under her own name, note the staple mix portion she received, any fresh food she took, and whether she ate eagerly, picked selectively, or was pushed aside. Scatter feeding makes individual intake harder to judge, so pair it with a short separate session for any mouse low in the group's order: five quiet minutes alone with her portion, a few times a week, gives you a true intake figure for the girl most likely to be short-changed. Note treats against individuals too. One mouse hoarding every high-energy extra while a cage mate thins is exactly the pattern a per-mouse feeding record exists to expose, and it is invisible in a line that just says the cage was fed.
Let the records tell you who needs a closer look
Read the two logs together, mouse by mouse. The combinations that matter are a falling weight alongside falling intake, which points to a mouse who needs separating at feeds and watching closely, and a falling weight despite good intake, which deserves a prompt conversation with your vet because eating well while losing condition is a change a mouse should not be left to ride out. A mouse who is hunched, rough-coated, or quiet at her usual active hour alongside a dropping weight should be seen the same day rather than waiting for the next scheduled weigh-in. Keeping every girl's weights, meals, and notes together in her KinsLe Pet Passport means the whole story of one small mouse is in one place when you, a sitter, or your vet needs to read it.