Barber’s Pole Worm (Haemonchus contortus)

Barber’s Pole Worm (Haemonchus contortus)
This is a very serious bloodsucking worm of sheep found to some extent for most of the year, but becoming most serious after extended dry periods, often in late summer and in autumn. Due to the warm wetter summer we are experiencing this year, we have already started to see cases.

It is called Barber’s Pole because of its appearance when seen in the abomasum of sheep – the worm’s spiralling red gut looks similar to the striped pole seen outside barbers’ shops. There is no other worm seen in sheep in New Zealand which looks like this. Adult worms are up to an inch and a half long and like small fibres of wool to look at. This is quite large compared to some other sheep roundworms but very small compared to dog roundworms, which most people will have seen.

Signs seen in sheep with severe Haemonchus infection are signs of anaemia (ie loss of blood). Younger sheep (lambs and two tooths) are usually the worst affected. They will lag behind the mob when they are being moved, and will have very pale membranes (white instead of pink).The worst cases can be expected to die even after treatment because the anaemia they suffer from can cause hypoxic damage to the liver – ie low oxygen through low ability of the blood to carry oxygen.

The seriousness of the problem we have with this worm stems from several factors:
  • It is a bloodsucker – sheep die from loss of blood. Therefore they can die quickly before you have a chance to save them.
  • It is extremely prolific – each worm can lay 10000 eggs a day to contaminate pasture. It also has a shorter pre patent period (ie the time from infection until the worm matures to lay eggs) than most other worms. It can be laying eggs in under 3 weeks.
  • Eggs can survive for long periods in dry weather on the pasture without hatching or dying. Because of this, huge numbers can build up before warm wet weather leads to the eggs hatching and becoming infective to sheep eating the pasture.
  • Immature worms suck blood – therefore new worms freshly picked up by the ewe/lamb can be causing serious anaemia and death within days.
  • Faecal egg counts are not a good indicator of the risk presented for the above reason.
  • Sheep do not scour due to Barber’s Pole – therefore dirty tails/dags are not a good reliable indicator of infection – lambs can have completely normal looking faeces and be dying from loss of blood due to this worm.
  • Most ordinary drenches will kill Barber’s Pole worms – but because they are not long acting, they do not completely control the problem
  • Resistance to drenches is found on some properties with this worm.
Means of Counteracting this Problem:
  • Drenching: this will limit the number of eggs laid down on the pasture, and limit their damage to sheep.
  • Long acting drenches throughout the summer and autumn – the best of these available contain Closantel eg Genesis Ultra. The downside of this is the long withholding period (56 days), which will interfere with your ability to send lambs to the works.
  • Medium acting drenches eg Cydectin/Vetdectin (Moxidectin). These have a shorter withholding period (10 days) which gives more flexibility to allow picking of lambs for the works but more frequent drenching.
  • Drenching with short acting drench and moving to known clean(er) pasture eg pasture only grazed by cattle over the last 6 months or so. This has implications for buildup of resistance of worms, and therefore needs to be managed carefully.
There are other diseases which can easily be confused with Barber’s Pole if post mortem examinations are not done to confirm the presence of the worms: these include Leptospirosis (which usually but not always has jaundice (yellowing) associated with it), some forms of plant poisoning, also some stages of Facial Eczema, and several other conditions.

If your lambs are due for a drench you should consider using a product that has some persistence for Barber’s Pole.

Date Added: Tuesday, 30th June 2015