Colin Trengove, Sheep Health Lecturer, UA Roseworthy campus:
SA is experiencing the climatologists’ prediction of a dryer than average autumn over much of the state and especially the south east. This is supposedly due to the tropical air being pushed further south causing northern Australia to be wetter than average and southern Australia drier than average. South easterners will certainly attest to that with little rainfall since October. Inevitably dry grass is scarce and heavy hand feeding of autumn lambing ewes is in progress.
Egg counts have been relatively low due to the extended dry in this environment, but as always it is vital to check your local situation rather than rely on general comments. In contrast, Adelaide hills and the mid north have seen spasmodic rainfall episodes since spring and so "hot spots" of significant worm burdens have been evident. This might only represent one in three mobs requiring a drench pre-lambing or before changing paddocks, but highlights that it is dangerous to extrapolate drench decision making between mobs. Invariably each mob is a unique worm risk case study and especially weaners and hoggets.
A little time spent collecting 20 individual dung samples from several mobs can well save the expense of much drenching leading up to lambing. However, it also requires hands-on knowledge of ewe condition to estimate their ability to withstand to risk of peri-parturient egg count rise i.e. worm burden increasing as ewe immunity wanes around lambing time. If you are confident that ewes are in good condition (score 3+) with reasonable nutrition ahead of them and egg counts less than 150 going into winter, then drenching can be avoided. If these criteria are not met, then drenching with a fully effective drench is recommended. This drench should be from a different group to that used at the start of summer to minimise the risk of encouraging drench resistance. It should also be given a couple weeks before moving the mob to a new paddock to further reduce the risk of resistance.