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Internal parasites in sheep
This material addresses aspects of the following syllabus outcomes:
H2.2 describes the inputs, processes and interactions of animal production systems.
The work presented in the following section contributes towards understanding the following syllabus content areas:
Students learn about:
Animal pests and diseases
- animal disease
- integrated pest management (IPM)
Extract from Stage 6 Agriculture Syllabus NSW Board of Studies Amended 2009
This work on internal parasites in sheep is made up of five sections with the following titles:
- Internal parasites in sheep (this section)
- Controlling internal parasites in sheep
- Resistance in sheep internal parasites
- Interpreting a drench label
- The effects of internal parasites: an experimental trial.
All these pieces of work are related and you will gain the maximum benefit by completing all of them. Even if you are not studying sheep, much of the theory applies similarly to the internal parasites that effect other species of animals.
Internal parasites in sheep
In an article in the February 1998 Farming Ahead journal, entitled 'Effective drench use reduces resistance, (pp 68-69) the following was stated.
The success of the Australian sheep industry is dependent on the successful control of parasites.
It has been estimated that 90 per cent of the cost of disease in sheep can be attributed to parasites.
Sheep worms cost Australian producers $222 million per year in production losses and deaths and control costs, including drenches and labour. This compares with $169 million for lice and $161 for blow flies.
Without the ability to control worms farmers would be faced with an inability to produce prime lambs of a saleble weight and wool cuts down to three to four kilograms per head compared with the current average of five to six kilograms.
Farmers with sheep with worms resistant to all drenches would experience neighbour hostility to sheep straying and lose their market for the sale of store sheep and breeding.
This is evidence of an important interaction between an animal production subsystem and the microbe/invertebrate subsystem. This interaction is the invasion of sheep by internal parasites. These internal parasites are commonly known as worms and are recognised as pathogens.
The four main internal parasites of sheep in NSW are:
- barber's pole worm (Haemonchus contortus)
- black scour worm (Trichostrongylus colubriformas)
- small brown stomach worm (Ostertagia spp)
- liver fluke (Fasciola hepatica).
The table below lists the effects of these four internal parasites of sheep.
| Parasite | Effects on sheep | Sheep most affected |
|---|---|---|
| black scour worm | burrows into the wall of the stomach and small intestine causing scouring, loss of appetite and condition, weakness, dehydration and death | weaners lambing and lactating ewes underfed sheep |
| small brown stomach worm | invades the wall of the sheep's fourth stomach causing scouring, weight loss and even death | weaners lambing and lactating ewes underfed sheep |
| barber's pole worm | feeds on blood from the wall of the sheep's fourth stomach, heavy infections cause sudden death from massive blood loss, most infections cause weakness, poor productivity, anaemia and bottle jaw | weaners lambing and lactating ewes underfed sheep |
| liver fluke | immature liver fluke migrate through the liver as part of their life cycle, this causes loss of appetite and condition, weakness, anaemia, bottle jaw and death | all sheep in the flock are susceptible to liver fluke |
Source: NSW Agriculture, Sheep Production Guide Book 5
Internal parasites are a major cost to the sheep industry. They reduce sheep farmer's income by:
- reducing lamb and wool growth rates
- reducing lambing and lamb weaning percentages
- increasing the number of sheep deaths, particularly among weaners
- the cost of treatment, both in drenches and labour.
Therefore, a farmer aiming to produce prime lambs and/or quality wool, needs to have an effective internal parasite control program, otherwise:
- the lambs will take longer to reach market requirements
- will fail to reach market requirements
- the wool will be of decreased quality.
Activity
Internal parsites can also be a major problem for the beef industry. Write down how you think internal parasites can reduce the income of beef cattle farmers.
If you would like to find out more about sheep internal parasites you should
investigate the NSW Agriculture 
web site.
Now try Controlling internal parasites in sheep
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