Worms in sheep: problem worms

Barber’s pole worm

This worm causes the majority of production losses and deaths in Queensland and is present in all sheep producing areas. Because female barber’s pole worms produce a large number of eggs (10,000 per day), infestations can quickly get out of hand. Worm numbers can increase very suddenly in warm humid weather. The worms rob sheep of valuable nutrition by sucking their blood and causing the loss of nutrients through the abomasal wall. Sheep carrying barber’s pole infections do not loose weight as sheep carrying scour worms do but they fail to gain weight. This results in reduced weight gains and wool cuts. Severely infested stock become anaemic and slow to muster. If anaemia is severe, a swelling under the jaw called ‘bottle jaw’ develops.

Acute or ‘spike’ infections often occur suddenly after periods of warm weather and scattered to heavy showers, when worm numbers can increase quickly typically from November to March when night time temperatures are above 20ºC. Daytime temperatures in Queensland are always suitable for worm development. Infective larvae can be available for ingestion in as soon as 4 days. Sheep may be in good body condition, but without warning become weak and likely to collapse if driven.

 Sub-acute ‘ongoing infections’ infections can happen any time, but they often occur a few weeks after a light shower. Sheep fail to gain weight and have poor body condition due to a gradual protein loss due to the infection. The worst affected sheep may have ‘bottle jaw’ (swelling under the jaw) indicating anaemia.

 

Worms in sheep: how they spread

Worm life cycle

Developing and mature barber’s pole worms live in the abomasum of the sheep’s gastrointestinal tract. Other worms such as the black scour worm and the nodule worm live in the small and large intestine respectively.

They mate and lay eggs which are then carried out with dung onto the pasture.

In the dung, eggs hatch into infective larvae.  If the dung remains moist, large numbers of larvae leave the dung pellet and move onto areas of pasture close to the ground.  Infective larvae are a waiting stage and as long as the environment around them is quite humid, they can survive about 3 months until eaten by sheep. Conversely, hot dry windy weather will shorten the life of infective larvae. Once in the sheep, the larvae develop and mature into adult worms and the cycle begins again. 

Worm infestations occur when large numbers of larvae survive on the paddock and are eaten during grazing. Any condition that causes dung to remain moist will promote the survival of larvae and provide a high risk of worm outbreaks.

Active barber’s pole larvae can survive in a dew drop waiting to be ingested.

Wet or humid weather

High risk weather is rain, storms or showers followed by about 4-5 days of cloudy or humid weather. The outer crust of dung pellets will be soft, enabling large numbers of worm larvae to move onto the green pick. During these high risk times, producers should increase their monitoring and testing, and be alert for signs of infection such as pink or white lower inner eyelids (red is healthy), reluctance to move and a “tail” forming on the mob when mustered.

Moist, sheltered areas

Even in prolonged dry weather, some conditions can cause dung to remain moist enough for larvae to survive and infect paddocks. For example, larvae can survive for long periods along bore drains, near dams and under trees.

Talk to one of our team at Vet Cross for advice on parasite control today. Prevention is better than cure.

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