Effective grazing management reduces the exposure of sheep to worms. There are three methods:
The last two are used to prepare ‘low worm-risk’ paddocks for lambing ewes and weaners.
Ewes temporarily lose some of their immunity to worms at and after lambing. As a result, they contribute greatly to the seasonal increase in worm numbers and subsequent infection of lambs.
Weaners are also highly susceptible to worms. Low worm-risk weaning paddocks give weaners a good start so they can build immunity without suffering high initial infections.
March and April: Prevent contamination with sheep worm eggs by spelling these paddocks, grazing with cattle or grazing with sheep for up to 21 days after the protection period of a drench proven effective on your property.
May, June, July and August: In some areas (e.g. tablelands), any stock including sheep can be grazed because it is consistently cold enough (mean daily maximum temperatures below 18°C) to almost stop the life cycle of the major roundworms (barber’s pole worm and black scour worm*). In warmer areas use the ’March–April’ strategy in those months where mean daily maximum temperatures are above 18°C.
Where sheep are referred to, include goats and alpacas, as they can carry sheep worms. While young cattle/calves also carry some sheep worms, adult cattle tend to have very low burdens of sheep worms and contribute very little to contamination of pastures with worms affecting sheep.
*Some development of black scour worms may occur until maximum temperatures fall below 15°C, but in this region barber’s pole worm control is the more important consideration.
An alternative method of lambing paddock preparation is ‘Smart-Grazing’. See Preparing lambing paddocks with ‘Smart Grazing—summer rainfall’.
Prevent contamination of the lambing paddock in the 6 months before the ewes enter the paddock. (For early autumn lambing, only 3 months preparation is required as larvae die faster in the preceding hotter months). During this 6-month period, sheep can be grazed on the lambing paddocks in months when mean daily maximum temperatures are below 18°C.
For the rest of the 6-month preparation period, the lambing paddock should be grazed by sheep for up to 21 days after the protection period1 of a drench known to be effective on your property.
In late spring and summer, larvae on pasture die faster than in the cooler months, so preparation of weaning paddocks takes about half the time required for spring lambing paddocks.
In the 3 months prior to weaning: Prevent contamination with sheep worm eggs by spelling these paddocks, grazing with cattle (especially to stop pasture from becoming rank) or grazing with sheep up to 21 days after the protection period1 of a drench known (from a DrenchTest) to be effective on your property.
Rotational grazing with short graze periods alternated with rest periods can greatly reduce the number of worm larvae on pasture, especially barber’s pole worm. While these systems (e.g. planned grazing, cell grazing, techno-grazing and intensive rotational grazing) are outside the scope of this publication, they use the principles found in Factors contributing to paddock contamination with worms.
1The protection period of a drench is when it is killing worms: 1–2 days for short-acting drenches, weeks or months for persistent products.