This sub tropically-adapted parasite prefers the warmer conditions of summer. It sucks blood from the stomach lining of naive sheep, and big burdens can remove enough blood to kill lambs and (less often) adult sheep.
It can ‘seem’ to strike without warning; mostly in late summer and autumn, though we do see the odd case prior to Christmas from time to time. Most outbreaks occur after a spell of hot, dry weather followed by some moisture. The textbooks say 25mm of rain, but a few heavy dews can be enough to spark it up.
With the right environmental conditions, and in the absence of effective management/control, ‘outbreak’ situations occur where larval numbers on pasture rise rapidly. Their ingestion by grazing sheep results in the sudden appearance of ill-thrift, lethargy and deaths.
One of the problems with Barber’s Pole is in predicting the seasonal onset of challenge. A study in the Manawatu found no correlation between farms for the timing and severity of Barber’s Pole challenge. Just because one farm had high levels, did not mean a nearby farm would be similar. And even on the same farm, the relationship between Barbers Pole levels in the ewes and lambs was weak.
Anyone who’s been caught by a decent Barber’s Pole outbreak can be forgiven for thinking it’s not worth taking the risk of leaving stock unprotected. But is it necessary every year? And what are the sustainability costs of doing this?
Could you better assess the situation on your place each year?
Other protective measures
Please ask if you need advice on which product is best for your flock.