There are mice on ISS. Not the first non-human mammals and likely not the last. Their health provides insights on influence of microgravity on organisms.
Very few humans stayed in space for longer than a year; after that period the health impact becomes too serious to allow them remain. What about mice, or other animals though? Have any stayed longer? And if so, what were the effects?
...I'm asking this in relation to the recent How much gravity is actually needed to avoid serious health consequences?. Building a centrifugal human habitat and letting the crew remain there well in excess of one year is impractical due to the cost. But building a centrifuge for some small animals? With mouse lifespan being only around two years, that wouldn't be too indicative, but guinea pigs reach age of 10, which should provide a plenty of data on influence of various levels of gravity on health.