Continuous grazing of a paddock increases pasture contamination and reinfection of livestock. Grazing management is an effective tool to help reduce the number of eggs being deposited onto pasture and the number of larvae being ingested by livestock. This ultimately reduces the reliance on chemical drenches and slows down the development of anthelmintic resistance.
When considering grazing management strategies there are two critical periods of equal importance. The 'graze' and the 'rest' period.
Figure 1: Even on recently-cultivated paddocks, worm larvae will accumulate rapidly and contaminate pasture for sheep or other livestock.
The length of time an animal spends grazing a paddock should not only consider the amount of feed available but the life cycle of the parasite species you are aiming to control paddock contamination with worms (wormboss.com.au). To achieve the latter, one should consider the autoinfection period, the time it takes for eggs (deposited onto pasture in faeces) to hatch into larvae and be ingested by stock. This can take anywhere between 4-10 days depending on worm species and environmental conditions. The aim is to graze stock for a shorter period than the autoinfection period. A short graze period will then prevent reinfection and lower parasite exposure which is especially important for our vulnerable young stock and pregnant and lactating animals.
To choose an ideal graze period you need to consider the lifecycle of the parasite roundworm life cycle (wormboss.com.au) you are targeting and the environmental conditions.
The rest period which is the time a paddock is rested from a single species of grazing livestock. This is because most parasites are host specific, such that most sheep parasites can only complete their life cycle inside sheep. The rest period also aids in breaking the parasite's lifecycle, by allowing eggs which have been deposited on pasture to hatch and the larvae to then die off without being ingested by livestock rotational grazing (wormboss.com.au).
Choosing the period of grazing and rest is a balance between worm control and pasture utilisation. It is important to consider the species of pasture present and the time of year. Faster growing pasture species and summer conditions will require a shorter rest period between grazing events. This is because pasture recovery is quicker and larval die off is accelerated in warmer months the effect of temperature on larval survival of barber's pole worm larvae on pasture (wormboss.com.au). While slower growing pastures and cooler conditions require a longer rest period scour worm larvae on pasture (wormboss.com.au).
For more details on grazing management to control worms, see the WormBoss page ‘Preparing low worm-risk paddocks’