In parts of the North Island, barber's pole worms (Haemonchus contortus) have been the cause of a lot of goat ill-health this year, and many goat owners will have suffered losses as a result of this nasty parasite. In this article, we explain what the disease is, and how you can make sure you don't have problems with it in future.
The main signs of infection are weakness and pale membranes. This is because Haemonchus worms live in the true stomach (the abomasum) where they suck blood. When there are many worms this leads to anaemia. There may also be diarrhoea and there may be bottle jaw (a soft swelling) between the mandibles under the jaw. Affected goats will also have lower growth rates and reduced fertility.
A complicating factor in the treatment and control of barber's pole worm infestations is that the worms may be resistant to some of the most commonly used worm treatments (anthelmintics).
Why is Haemonchus called 'barber's pole' worm?
Adult Haemonchus contortus worms are about 2 to 3 cm long. Their blood-filled intestines spiral from the mouth to the tail end, so the worm can look like a barber's pole.
Adult Haemonchus worms live in the abomasum, where they mate. The females lay up to 10,000 eggs a day that pass out onto the pasture in faeces. Larvae hatch from the eggs and migrate up the pasture to be ingested by goats as they graze. In the abomasum, the larvae mature and the adults attach themselves to the lining of the stomach to feed on blood.
A heavily infected goat can bleed to death within a few days. Mild wet autumn weather and high stocking rates increase the risk of heavy infestations.
Controlling barber's pole worm
The best control strategies involve three components:
- Use of effective anthelmintics
- Improved herd and pasture management practices
- Use of pasture species with anthelmintic properties
Use of anthelmintics to control worms
Anthelmintics are widely used to control worms such as Haemonchus. Some anthelmintics have been officially approved for use in goats and this will be indicated in the instructions for use on the packaging. However, some of the 'approved' anthelmintics have become ineffective because Haemonchus has become resistant to them. There are other types of anthelmintic that will be effective but they may not have been officially cleared for use in goats. For these reasons it is important to consult your veterinarian to help you select the appropriate anthelmintic to use, the correct dose to give, the route of administration, duration of effect and possible adverse effects. It's also very important that you note the withdrawal period - ie the length of time that must elapse before you can use meat or milk from the treated goats.
Your veterinarian can also arrange for faecal egg counts - they can be used strategically to indicate the size of any worm burdens, to test drench effectiveness and to identify drench resistance.
Management to control worms
There are various management practices and combinations of these that are very useful for controlling worms in goats:
- Keep stocking rates low
- Provide clean water, and mineral supplements as appropriate
- Use clean feeders and continue to practice good hygiene in the pens and pasture.
- Use gravel or concrete in feedlot areas
- Provide good-quality hay instead of pasture and keep hay off of the ground to avoid contamination by faeces.
- Incorporate browse plant species when possible
- Graze other species with your goats, eg cattle or horses
- Use pasture for hay-making.
- When possible, alternate the pasture with a short cycle crop, such as hay. This will help to decrease larvae population in the pasture and prevent re-infestation. Direct sunlight during the summer months or during freezes in the winter will help decrease the population of larvae that remain in the soil.
- De-worm does soon after they have kidded. The hormones of pregnancy suppress the doe's immune system and worm burdens can build up during pregnancy and lactation.
Use of plants with anthelmintic properties
Forages, such as clover, vetches, and chicory contain condensed tannins. Condensed tannins reduce the number of stomach worms and suppress egg production.