Merial Warns Farmers To Beware Of Barber's Pole Outbreak
Merial New Zealand is promoting on farm parasite management plans and advising farmers to hone up on their knowledge of
Barber's Pole worm and its debilitating effect on sheep mobs.
Merial Veterinary Technical Service Manager Justin Hurst says Barber's Pole, or Haemonchus, is a seasonal worm which
tends to overwinter as low numbers of adults in sheep, only to feature as disease outbreaks in the warm moist late
summer period.
He says the Haemonchus outbreak scenario can be prevented by a parasite management plan incorporating the provision of
low parasite larvae pasture and a structured drenching programme over the summer period.
"It's important farmers understand the two main reasons why outbreaks of disease occur. First, the long uterus of the
female may produce thousands of eggs per day - some texts quote up to 10,000. Also, given ideal sub tropical conditions,
they can grow to infective larvae in just one week.
"Secondly, unlike most intestinal worm species that slowly debilitate the host as the gut reacts to the adult worm
burden, large intakes of Haemonchus larvae can literally bleed a sheep to death before they even lay a single egg. "
He says relying on faecal egg counting may be inadequate for monitoring Haemonchosis.
"Sheep, particularly lambs but all age sheep, may succumb if faced with a large larval intake, and need to be observed
for classical blood loss signs like lethargy and paleness of the eyes and gums."
Barber's Pole, or Haemonchosis, is literally an infection of blood eating worms. It gets its common name from the
intertwined blood filled intestine and equally long uterus of the female. Several thousand worms, less than a small
handful, each only around 15-30mm long, constitutes a burden that if not fatal, may prove highly production limiting to
the young or weak host sheep.
Hurst says drenching with a non persistent triple active combination such as TRITON® will minimise the selection of worm
species present due to its excellent efficacy (>99.9%) against the resident population, and no selection for incoming
resistant larvae in the days or weeks following drenching.
"In the face of Haemonchus outbreak," says Hurst, "all stock need to be treated and preferably moved to a paddock of
known nil or low Haemonchus infectivity. Often this "clean" paddock is purely fictional within the constraints of
practical farm management, and using a product with persistent activity against Barber's Pole becomes the only realistic
option."
Persistent activity options are the IVOMEC Maximizer® capsule, a moxidectin containing drench or a closantel containing
drench. The Maximizer will supply an even level of ivermectin over a 100 day period, while moxidectin and closantel
products provide reducing levels over time as they are removed from the fat and blood respectively.
Irrespective of the product used, Hurst says the flock needs to be monitored for re-infection. This may be related to
resistant worms, or variation between formulations.
"The closantel-containing formulations registered in New Zealand have persistent activity claims ranging from zero to 42
days, related to closantel type and concentration, so check the label and the withholding period. And be aware of dosing
error. It happens!"