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Internal Parasites

  • Helen Simmonds, "Rowan Park", NSW

Goats may suffer from infestations of worms, liver fluke, coccidia, yersinia and other internal micro-organisms, either separately or con-currently. Early recognition is necessary to maintain good herd health. The effects of internal parasites are compounded by the goat's low threshold to any stress, where they may die as a result of secondary parasite attack, rather than the actual initial trauma.


The worm species of major economic importance to the goat production are:

  • Barbers pole worm (Haemonchus contortus)
  • Black scour worm (Trichostrongylus species)
  • Brown stomach worm (Ostertagia species)

Other worm species may become of economic importance in isolated cases. These include:

  • Nodule worm (Oesophagostomum spp)
  • Small lung worm (Muellerius cappillaris)
  • Tape worm (Monezia species)
  • Liver fluke (Fasciola hepatica)
  • Stomach fluke (Paramphistomum species)
  • Thin necked intestinal worm (Nematodirus)

These worms can be classified according to the mechanism they use to cause ill health. These mechanisms are:

  • Blood sucking
  • Interference with nutrient absorption via damage to gut lining
  • Migration through tissues

Parasites which suck blood

Barbers pole worm and adult liver fluke feed on blood causing severe anaemia in the goat. This is observed initially as paleness of the skin and mucous membranes in the mouth and eyes. As the anaemia becomes more severe a soft swelling develops under the jaw (bottle jaw), and animals may collapse on mustering. With heavy worm burdens, goats may become too weak to respond to treatment, and die. Unless close observations are made, these signs are often overlooked and the mob will have an endemic problem.

Parasites which damage the gut lining.

Many parasites damage the gut lining, thus depressing appetite and interfering with absorption of nutrients. The most important of these are the black scout worm and the brown stomach worm. Heavy burdens of small intestinal worm and immature stomach fluke also produce severe weight loss and death in isolated cases. Nematodirus burdens may be observed after rains, which break a prolonged dry spell in semi-arid areas.

With black scour worm and brown stomach worm infestations there is an initial loss of appetite and gradual loss of condition, although the first sign usually seen is scours, (diarrhoea). These scours are usually dark green, and may be profuse, staining the breach area. Goats may show signs of colic, and separate from the mob. Malnutrition and dehydration lead to death. Signs of pneumonia may also be observed in the terminal stages. Anaemia is not a feature of this parasite burden.

Recovery may be delayed by reinfestation after treatment, by emergence of immature forms from the gut wall after treatment (brown stomach worm) or by the presence of coccidia infection (see also coccidiosis).

Parasites which migrate through body tissue and organs

Immature stages of lung worm and live fluke migrate through different body tissues or organs causing considerable damage.

Migrating lung worms cause coughing. Adult small lung worms (Muellerius) cause nodule formation in lung tissue, which can lead to collapse of small areas of the lung. Adult large lung worms (Dictyocaulus spp) infest the large airways causing coughing and pneumonia.

With liver fluke migration, an acute illness may occur. Goats may be jaundiced with a yellow discolouration of the mucous membranes of the eyes. Some animals may scour and die. With long standing infestations, goats show signs of anaemia, bottle jaw, pale skin and eyes, and sudden death.

Seasonality and Distribution

Barbers pole worm requires heat and humidity for the developing stages (eggs and larvae) to survive on pasture. It is found in wet summer areas, and will cause problems year round in sub-tropical climates with uniformly warm and wet seasons.

Black scour worm and brown stomach worm larvae require cooler temperatures to survive on pasture, and produce heaviest burdens during wet, cool seasons. These parasites cause problems in regions with mild wet seasons.

Goats often suffer from a mixed burden of the most important worm species. Heavy infestations of one variety, leads to a run-down condition where they may succumb to another worm infestation, and die a few months later.


There are four or five main drench groups, or anthelmintics, which are aimed specifically at different groups of parasites.

Broad spectrum drenches fall into two categories according to their mode of action.

  • Benzimidazoles (BZ) group, inhibit the worm's energy system
  • Levamisole/morantel (non BZ) group paralyse the worms nervous system
  • Narrow spectrum drenches are also grouped according to their mode of action.
  • Organophosphates interfere with the nervous system
  • Salicylanilides become bound to the animals blood proteins and effectively inhibit the energy system in blood sucking parasites. (Hence narrow spectrum activity)
  • The "Mectins" are the last alternative.

Not all these drenches may be registered for use in goats in all states. Owners should check these with their local Department of Agriculture, or Rural Lands Protection Board (or similar), before use.

New South Wales has several "strategic drenching programs" used in different parts of the state. Eg, "Worm-a Goat", "Drenchplan", "Wormkill", each of which is tailored to the local conditions, and enables goat growers to work together if necessary.

Control Methods

Chemical Control

Most goat growers rely solely on drenches for worm control. These should be used to suit the local seasonal pattern and stocking rate on farm.

There are some basic principles to maximise the use of drenches.

  • Avoid underdosing any goat in the mob, dose to the heaviest animal.
  • Check the accuracy of the drench gun
  • Drench all goats on the same day
  • When giving two drenches, give separately, to avoid adverse reactions.
  • Move drenched stock to a clean paddock, after allowing the last goat to empty for four hours after drenching.
  • Collect and test faecal samples at regular intervals to monitor control methods.

Non Chemical Control

These systems are based on the reduction of larval contamination on pasture.

  • Pasture spelling, minimum two months under hot dry conditions, or six months under cool moist conditions.
  • Pasture cropping or cultivation
  • Alternate grazing of paddocks at regular intervals with other species, eg horses or cattle, NOT sheep.
  • Paddocks with good browse are more suited to worm control in goats than are pasture grazing paddocks. Worm larvae are only found on pasture up to about ten centimetres above ground level.

Grazing Management

Drenching programs will fail if properties are over-stocked, or there is too little pasture in a dry season. Worm burdens on pasture can be reduced if goats are drenched and moved to "safe" paddocks. Newly drenched goats will very quickly pick up worm larvae from contaminated paddocks, and will be no better off, and the owner will have wasted his time and money.

Drench Resistance

Drenches are only highly effective against susceptible worm species. Underdosing or high frequency drenching may lead to worms developing varying degrees of resistance to a particular drench group. If the above reasons for failure to respond to a drench can be eliminated, drench resistance may be suspected. The problem should be investigated, with veterinary advice, and alternative worm control strategies may need to be used.

© 2000 A.C.G.A.