Utilising Forage Crops for Growth and Parasite Management

We all know drench resistance is now widespread on New Zealand sheep properties. While drenches remain an important tool, long-term parasite control and farm profitability increasingly depend on nutrition, grazing management, and the strategic use of forage crops. When used well, forage crops not only reduce worm challenge but also significantly lift lamb growth rates and allow earlier finishing – thus reducing exposure to resistant parasites altogether.

Why forage crops deliver both growth and parasite benefits

Most economically important sheep parasites rely on ryegrass–clover pastures to complete their lifecycle, with larvae surviving best in moist swards close to the soil surface. Forage crops disrupt this cycle while simultaneously delivering higher quality feed than summer pasture.

Key advantages include:

• Higher protein and energy intake: supporting faster liveweight gain
• Earlier development of worm immunity: due to increased protein intake
• Faster lamb finishing: more lambs sold before peak parasite challenge in late summer
• Lower pasture larval intake: better growth and reduced drench requirements.

The immune system relies heavily on protein to build resistance to worms. Lambs must first meet their protein requirements for growth before any excess can be diverted to immunity. On high-protein forage crops, lambs can start developing effective worm immunity at around 30kg liveweight, compared with closer to 40kg on a conventional grass-based system.

What’s hot… Worm vaccines are on the way! A vaccine has been developed against Barber’s Pole and will soon be commercially available. They are working hard to extend this to other species of worms in cattle, sheep and deer. Watch this space!

In practical terms, this means lambs on forage crops grow faster, cope better with worm challenge, and can be finished and sold earlier – often before resistant worm populations peak.

Forage crops that work well for lamb growth and finishing

• Brassicas (kale, swedes, rape, leafy turnips): Brassicas provide high-quality, highly digestible feed that drives excellent growth rates. They are usually ready to graze from February, which is when resistant parasites start ramping up (commonly Trichostrongylus).
• Chicory and plantain: These forage herbs consistently support high lamb growth rates through summer and autumn. Benefits come from lower larval intake, rapid leaf regrowth, and possible direct effects on parasite survival. Lambs grazing chicory or plantain often finish earlier and require fewer drenches compared with those on pasture.

Management makes the difference

The growth and parasite benefits of forage crops are quickly lost if crops are poorly managed. Key principles include:

• Weed control: Effective herbicide use is essential. Weeds create a moist canopy where larvae can survive, undermining the “clean feed” effect.
• Crop choice: Work with your agronomist and veterinarian to match crop species to soil type, rainfall, farm system, and labour availability. High-country properties may also need to consider contractor access and availability.
• Headlands and run-offs: While the crop itself may be low challenge, surrounding areas can still carry worms. Lambs grazing crops still require faecal egg counts (FECs) and occasional drenching, but drench intervals are usually much longer.

“By shortening the time lambs are exposed to parasites and improving overall performance, forage crops can play a major role in slowing parasite resistance and improving farm profitability.”

Using forage crops without increasing resistance risk One risk of clean-feed systems is over-selection for drench resistance if all worms are exposed to treatment. To protect refugia:

• Leave a proportion of lambs undrenched before moving onto forage (where appropriate and closely monitored) or return lambs to old pasture after drenching before shifting to crop.
• Consider delaying post-weaning drenches if lambs are growing well on low-challenge forage.
• Use FECs to guide drenching decisions rather than calendar-based programmes.

Take-home message Forage crops are not a stand-alone parasite solution, but they are one of the most effective tools available to lift lamb growth rates, finish lambs earlier, and reduce reliance on drenches. By shortening the time lambs are exposed to parasites and improving overall performance, forage crops can play a major role in slowing parasite resistance and improving farm profitability.

Work with your veterinarian and agronomist to integrate forage crops into a whole-farm parasite and nutrition plan that suits your system, climate, and resistance status.