It means we don’t have to worry about predators:

What is really interesting is that domesticated rodents, such as mice and rats bred for laboratory use or for the pet trade, do avoid faeces [as opposed to wild rodents, which prefer poo]. As wild reindeer and primates also avoid faeces, domestication isn’t the key, so what is it? [The University of Edinburgh’s Patrick] Walsh and colleagues believe that for their wild mice, the presence of faeces from other mice at a potential nesting location or near food suggests safety from predators. When the wrong move could land you between the teeth of a bigger animal, perhaps the risk of infection from faecal matter is the lesser of two concerns. Laboratory animals, pets, and livestock are generally at a much lower risk from predators than their wild counterparts, so they can be more selective in their foraging and nesting behaviours. Every animal, the researchers argue, must calculate the trade-off between dodging parasites and surviving another day.