Animal waste is removed from a barn floor by moving a trolley in a first direction adjacent a first trough in the floor. As the trolley moves in the first direction: a blade extending from the trolley scrapes the waste into a region adjacent the trough; rotating paddles on the trolley drive the waste from the region into the trough; and a plow on the trolley that extends into the trough drives the waste toward one end of the trough for removal. Alternatively water drives the waste in the trough in the first direction. When the trolley moves away from the one end, the blades scrape the waste toward the region and the paddles drive the waste into the trough, but the plow is idle because the plow pivots to ride on top of the waste.