to clean the place where a large animal lives {e.g. stables}
For a bit of extra money she helps muck out a friend's racing stables.
muck out
verb to kill US, 1984
phrasemuck out muck out • muck out sth • muck sth outBrE to clean the place where a horse or a farm animal lives: There's a lot of hard work involved in having a horse - mucking out, feeding and grooming.Charles spent a week working with a farmer - he even mucked out cattle yards and fed the pigs.