Rotating enrichment, not adding more of it, makes rats more optimistic, a study shows
Published by Planète Pets · managing editor: Clément Lacaille · how our guides are written
Faced with an ambiguous situation, an animal can respond with optimism or with wariness — a difference measurable in the lab through a judgement-bias test. A German study published in 2025 looked at what, in a cage’s enrichment, actually shapes that outlook on uncertainty in rats. Our other enrichment guidance is gathered in the rodent toys and enrichment section.
Contents · 5 sections
Consistent enrichment versus regularly changed enrichment
Published in Scientific Reports by Groneberg, Hoppe, Richter and Kaiser, of the University of Münster, the study housed female Lister Hooded rats for several months under either consistent enrichment or regularly changed enrichment — broadly the same types of items, but swapped at set intervals rather than left identical (see the study, doi 10.1038/s41598-025-22088-x). At the end of that period, the rats took a judgement-bias test, based on interpreting ambiguous cues, which classifies them as leaning optimistic or pessimistic in the face of uncertainty.
Rotation, not quantity, makes the difference
Rats in the regularly-changed-enrichment group responded more optimistically to ambiguous cues than those in the consistent-enrichment group. The total amount of enrichment items wasn’t the distinguishing factor between the two groups: it was periodically changing what was already present in the cage that made the difference on this cognitive test.
What this means for a cage at home
For a pet rat, this result supports regularly rotating equipment already owned — tunnels, hideouts, chew items — rather than piling up accessories that never change. Cycling two or three sets of enrichment week to week, rather than constantly buying new items, follows the same logic tested in the study. This principle complements our guidance on rough-and-tumble play in rats and on tickling dosage, two other documented levers of behavioural enrichment in this species.
A limit worth keeping in mind
The study measures a behavioural judgement bias, not a stress hormone directly, and covers laboratory rats of a single strain. Regular rotation remains a reasonable approach at home, though the study itself doesn’t set a precise rotation schedule.
Frequently asked questions
Do old toys need throwing out to buy new ones every week?
No, the study is about rotation, not permanent replacement: cycling an existing stock is enough to reproduce the principle tested.
Does this result also apply to other rodents besides rats?
The study specifically covers rats; the principle of variation is plausible in other curious species such as mice, but hasn’t been measured the same way. Find all our guides on the rodent hub.
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This guide is part of Planète Pets’s Rodents universe. Our advice is general in nature: for any health concern, your veterinarian remains the only reference.
