A routine step before surgery—gently handling mice so they become used to people—did not simply make recovery better or worse. Its effect depended on who the mice were and where they lived afterward. These imaging windows let researchers watch living organs repeatedly, but placing one requires surgery that causes physiological stress and may influence experimental outcomes.

That creates a problem: the processes researchers want to study, including inflammation, immune cell behaviour, and tissue remodelling, are themselves highly susceptible to surgical stress and peri-operative management. So the study examined how handling before surgery and housing after surgery affected welfare and immune measures in mice with a kidney imaging window, across both sexes.

The researchers assessed body weight, clinical health scores, circulating white blood cells, a urine measure linked to stress, and immune cells in the kidney over the recovery period. The study asks whether pre-operative habituation changes physiological responses after surgery, because its effects on post-operative physiology remain incompletely understood.

After surgery, some mice lived alone and others stayed in groups, so the study could examine whether the surroundings after surgery changed the effect of earlier handling. The clearest body-weight change appeared in males: those handled beforehand lost more weight after surgery than males that had not been habituated.

Handling beforehand also delayed weight recovery in group-housed males, while females showed comparable weight trajectories regardless of habituation or housing condition. But body weight was not the whole story. Across immune and hormone-related measures, the predominant effect was a change in how much individual animals differed from one another.

In other words, the main result was often not a shift in the group average, but a change in the consistency of responses across animals. The housing arrangement mattered. Among group-housed mice, those habituated before surgery showed less variation in white blood cell counts, the urine stress measure, and immune-cell presence in the kidney.

For individually housed animals, those effects were absent or reversed, showing that the same pre-surgery handling did not produce one fixed result. Taken together, pre-operative habituation changed post-operative immune and hormone-related responses in a way that depended on both sex and housing.

It affected both the size of the response and the variation between individual animals. The study therefore treats differences between individual animals as a meaningful biological result, not merely as statistical noise. Under suitable housing conditions, handling beforehand made immune and hormone-related responses more consistent without necessarily changing the average group response.

Reducing avoidable stress-related variability could improve experimental sensitivity, especially because immune and endocrine measurements are common endpoints in intravital microscopy. The central lesson is that reducing stress before surgery can make biological responses more consistent, but only under the right housing conditions.

That matters because consistency can make animal research easier to interpret and may improve welfare.