Does rotational grazing help reduce the number of worms on pasture? Does grazing sheep and cattle together help manage worms? How long do I need to wait for worm larvae numbers to drop before grazing a paddock again? You’ll find the answers in this section!
Techniques that can be used to reduce worm challenge to susceptible stock include:
- Grazing only the top 1/3 of the pasture with your vulnerable young stock.
- Using adult stock and other species of stock to clean up behind youngsters and increase the time taken for them to come back to the same ground.
- Removing larvae in hay and silage.
- Spelling paddocks for prolonged periods.
Grazing height
See ‘Worms on pasture/Where do the larvae live’ for the lowdown on how grazing height affects worm larvae intake.
- The less that lambs and calves have to graze down beyond the top 1/3rd of the pasture, the less worm larvae they will consume.
- They’ll also grow faster; more quickly reaching a size and maturity where they can manage some worm challenge on their own.
- Immune, adult stock, or another species, can be used to ‘groom’ the pasture in rotation behind the youngsters.
Rotations
- Young stock rotating around their own block with no adult stock or alternate species to cross-graze, can, in time, build up higher and higher levels of worm contamination on pasture.
- This can be even worse if most of the worms being built up are drench survivors (drench-resistant worms).
- In general, the longer taken for young stock to rotate back to the same area, the lower the level of worm challenge they will face when they get back.
- This occurs partly because larvae on the pasture die off over time, but mostly from the action of other stock classes and species removing larvae as they graze.
‘Leader-follower grazing’
- In this system, grazing is planned so that the most vulnerable mob (say lambs, or 100kg calves) is the ‘leader’ mob
- Less vulnerable animals (say ewes and R2 cattle) follow behind to groom the pasture and ‘vacuum up’ worm larvae.
- Some farmers also call this a ‘truck and trailer’ system.
It's important in these systems to also watch that the follower mobs are being well-fed so that their own immunity to worms is not compromised. The ‘vacuum cleaner’ ability drops off when under-feeding kicks in!
Photo credit: John Ford, Highlands Station.
Cutting for hay and silage
- Cutting grass can remove some of the worm larvae.
- However, given that most larvae live in the lowest parts of the pasture, cutting for hay and silage won’t remove all of them.
Silage
- Usually cut when grass is still green and actively growing.
- Silage paddocks may re-grow to their original height within a few weeks of being cut.
- Under these conditions, the remaining larvae can be quite well protected.
- Recent on-farm monitoring work has shown that it’s common for lambs grazing silage aftermath to become infected with worms again quite quickly.
Hay
After cutting, the remaining sward is often more open than in silage paddocks.
More sunlight gets to the base of the pasture and (especially in dry summers) - more larvae die from heat and drying.
The grass can take longer to re-grow – more larvae die of over time.
So re-grown hay paddocks may have lower larval levels on them.
See Crops and forages for guidelines on managing swards with low larval levels.
Photo: Tempello Station, Marlborough.
Pasture spelling
Under NZ grazing conditions, spelling pasture is rarely a practical way to reduce larval numbers. It takes months, not weeks, for larval levels on pasture to drop simply because of time.
The exception is extreme hot and dry conditions:
- L3 larvae do not feed – they rely on stored metabolites to survive.
- In warm conditions, the larvae use up their stored energy quite quickly.
- With adequate moisture they may last month or two.
- But if it dries out quickly, they may only survive a few weeks in the heat.
- Don’t forget, some will survive in the soil.
In cool conditions, larvae use up their stored energy more slowly and it may take 3-6 months for numbers on pasture to drop enough to make a difference.