Forage harvester

How it works

Crop enters through a header at the front. For grass, a pick-up lifts a wilted swath left by the mower and rake; for maize and whole-crop cereals, a cutting header severs the standing plants directly. Feed rollers then squeeze the crop into a firm mat and push it into the cutterhead, a heavy spinning drum with knives that chop against a fixed shear bar. The feed roller speed sets the chop length.

After chopping, maize usually passes through a kernel processor: two toothed rollers pressed hard together by springs that crack the grains so cattle can digest the starch. For grass the processor can be swapped for a plain chute. A paddle accelerator, or blower, then throws the material up through a swivelling spout into the trailer.

Main types

• Self-propelled forager: The modern standard for contractors. The largest machines have engines above 1,000 hp and can fill trailers at several hundred tonnes an hour.
• Trailed precision-chop harvester: Pulled and PTO-driven by a tractor, with a cutterhead that gives an even chop. Still used on smaller farms.
• Single-chop and double-chop harvesters: Simpler trailed machines that cut with a flail or rotor. Cheaper, but the chop is longer and less even.
• Grass pick-up header: A wide tined reel that lifts swaths cleanly. Widths of three to over four metres are common.
• Maize header: Rotary drums or row units that cut maize regardless of row spacing. The widest cover a dozen or more rows.

Hooking it up to a tractor

Trailed foragers hitch to the drawbar and take all their power from the 1,000 rpm PTO, with hydraulics to swing the drawbar and steer the spout. Because chopping takes a lot of power, they need a large tractor. Self-propelled foragers need no tractor of their own but rely on a fleet of tractors and silage trailers to shuttle the crop to the clamp.

A short history

Early harvesters were towed machines that cut, chopped and blew crop into a trailer hitched behind or driven alongside. Controls moved from cables to hydraulics and later to electronics, and towed single-chop and double-chop machines gave way to precision-chop designs with a cutterhead. Self-propelled models now do most contract work; Claas, which dates its forage harvester line to 1973, offers Jaguar machines of up to 1,110 hp with 10.5-metre maize headers.

Buying and care tips

• Keep knives sharp: Sharpen the knives and set the shear bar close daily. Blunt knives raise fuel use and give a ragged chop.
• Get the chop length right: Short chop packs well in a clamp; longer chop gives cattle more fibre. Agree the target with whoever feeds the silage.
• Check kernel processing: Collect a sample and look for cracked grains. Uncracked maize kernels pass straight through the animal.
• Watch for stones and metal: Metal detectors and stone guards protect the cutterhead. Test them before the season starts.
• Plan the trailer fleet: A forager is only as fast as the trailers serving it, so match trailer numbers to haul distance.

Questions people ask

What does a forage harvester do?

It cuts or picks up green crops, chops them short and blows them into a trailer so they can be made into silage.

What is a kernel processor?

A pair of toothed rollers behind the cutterhead that crack maize grains. Cracked grains are digested far better by cattle.

Can a forage harvester do grass and maize?

Yes. You change the header: a pick-up for wilted grass and a maize header for standing crops. The kernel processor is usually removed or bypassed for grass.

What is the biggest forage harvester?

The largest self-propelled machines, such as the Claas Jaguar 1200, produce over 1,100 hp.

Related equipment

Sources

1. Forage harvester, Wikipedia (IPFS mirror)
2. Forage harvesters, Claas
3. Claas unleashes 1,110hp Jaguar 1200 forage harvester, Farmers Weekly

Last checked 2026-11-01

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