More about acquired immunity to worms
- Immunity is rarely complete, so even immune sheep carry a few worms. However, immunity reduces worm numbers and production losses.
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The time taken for immunity to develop depends on the age and nutritional status of the sheep, whether it has been exposed to worms previously and the number of worm larvae it is exposed to. Immunity will help to ensure that:
- Fewer incoming worm larvae establish and become adults;
- Established female worms lay fewer eggs; and
- Established adult worms are rejected by the sheep.
- Exposure to worms is needed for immunity to develop and to be maintained. There must be sufficient exposure to stimulate the immune response, but not to the degree where the animal is overwhelmed, which would result in production losses or disease.
- Immunity to worms affects worm burdens in three stages.
- When a sheep develops immunity to one species of worm it is sometimes also immune to other worm species.
- How a sheep's immune system removes worms is not fully known.
- Immunity to worms requires extra nutrients. In young worm-infected sheep, nutrients are diverted from muscle and wool growth to developing an immune response to the worms.
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