Build the baseline during a healthy week
Choose a week when your rat is unmistakably himself, and write down what normal actually looks like for him in four short categories: eating, droppings, activity, and breathing. Rats are individuals — one is a dawn grazer, another does his serious eating at midnight — so the baseline has to describe your rat, not a textbook rat. Note how much of his staple mix disappears in a day and which ingredients he leaves, what fresh foods he takes eagerly, and how quickly he comes to the cage door at feeding time. A rat who has always left the same ingredient is not a worry; a rat who suddenly leaves everything is, and only the written baseline lets you tell those two apart with confidence.
Write down what normal droppings and activity look like
Healthy rat droppings are firm, oval, and fairly uniform, and a cage cleaned on a routine gives you a steady picture of how many he produces. Note the normal size and consistency, and anything that is normal for him alone, such as softer droppings after particular vegetables. Activity needs the same treatment: record when his busy hours fall, how he climbs, whether he uses his whole cage or favours one level, and how he behaves during free-roam time. Add two quiet details many owners miss. Rats produce a red discharge called porphyrin, and a small amount around the eyes and nose after sleep can be entirely normal for him — note his usual amount. Note, too, that his breathing at rest is normally silent, so his baseline page should say exactly that.
Log changes in the same words each time
After the baseline week, keep the record going with a brief daily line, always using the same simple scale so entries compare cleanly: appetite all, most, half, or none; droppings normal, soft, fewer, or none seen; activity usual, quieter, or hiding. Same words, same time of day, ten seconds of writing. This is what makes a change stand out early instead of in hindsight. When you look back and see appetite slide from all to half across three days while the droppings shrink, you are looking at a trend with dates on it — not a worry you talked yourself out of because any single day seemed explainable.
Know which changes mean a prompt vet call
Rats hide illness well and can go downhill quickly, so the baseline ends with the thresholds you have decided in advance. A rat who stops eating, produces no droppings, sits hunched with a rough coat, or breathes noisily or with effort is not a wait-and-see case: that combination means a vet the same day. Increasing porphyrin that he is not grooming away, one-sided discharge, or a new lump noted during handling all belong in the log with a vet call booked rather than watched indefinitely. You are never diagnosing from the notebook; you are using it to notice sooner and to describe precisely. Filed in your rat's KinsLe Pet Passport, the baseline and its daily lines give your vet a clear, dated history instead of a guess about when things changed.