An agricultural vehicle including a chassis and a header carried by the chassis that includes a cutterbar assembly with a plurality of cutting units. Each of the cutting units includes a rotatable disc carrying a plurality of knives each defining at least one cutting edge and a guard assembly including a plurality of extensions. Each of the extensions includes a bottom guard portion connected to a top guard portion to define a knife slot that allows the plurality of knives to pass through during rotation of the disc. At least one rotary driver couples to the rotatable disc of at least one of the cutting units.