A manure spreader includes a box for containing manure. The manure spreader box includes a bottom wall, a front wall, two side walls, and a manure discharge opening. The manure spreader also includes a wheeled frame supporting the box, and a vertical beater assembly for engaging and expelling manure. The vertical beater assembly includes a first vertical beater rotatable about a first axis and includes a shaft having a first flighting forming a left-handed helix, and a second flighting forming a right-handed helix. The manure spreader also includes a manure transfer mechanism for moving manure contained in the box to the manure discharge opening for engagement with the vertical beater assembly.