Answers:

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1. Typically what proportion of the total cost of worms is attributed to production loss, rather than control costs?

The impact of roundworms represents the highest animal heath cost to the Australian sheep industry. Typically, lost production accounts for over 80% of the total cost with control accounting for less than 20%.

2. What is the length of the prepatent period of typical roundworms and how can the prepatent period be used to advantage?

This is the time taken for infective larvae, eaten by a sheep grazing pasture, to develop to adult worms in the gut, mate and start laying eggs, which appear in dung. The time depends on the worm species with barber’s pole worm completing this period in a minimum time of 18 days under ideal conditions. Most scour worms take about 21 days.

Therefore, little, if any, worm egg contamination of pastures will come from sheep in the pre-patent period from a few days after they have been given an effective drench that kills 98% or more of the worms present. Allow sheep to graze up to 21 days in barber’s pole worm areas and to 30 days in southern scour worm areas. This is a principle used in ‘Smart grazing’.

3. Are worm eggs able to wait for months and then hatch when conditions are favourable?

As worms require both warmth and moisture for eggs to develop to larvae (above 10–18°C depending on worm species, but ideally below 35°C, and with usually more than 15 mm rain over 4–7 days of rainy or overcast weather when the evaporation rate is low), there can be extended periods of the year in some locations when worms cannot successfully complete their life cycle. These include regions with particularly cold winters or hot summers or where there are lengthy dry periods.

Barber's pole worm eggs will die if these conditions are not met within about 10 days of them being deposited on the pasture. Scour worm eggs are able to survive a few more weeks awaiting suitable conditions for hatching

4. Which age of sheep are most prone to hypersensitivity scours and why?

Hypersensitivity typically occurs in the winter and spring months, in animals that have developed their adult worm immunity, and is most evident in mature ewes or wethers. In south-east Australia scouring occurs in a large proportion of some flocks (30–40%) every year, and may last for 3–4 months. In Mediterranean climatic zones, hypersensitivity scouring usually occurs after the relatively worm-free period of summer and autumn, after sheep are re-exposed to worm larvae. The occurrence between flocks and years varies considerably, and it generally lasts for only 4–6 weeks in a particular flock.

5. Name two common signs associated with a severe infection of either barber’s pole worm or liver fluke.

Severe acute or ongoing (chronic) blood loss from either barber’s pole worm or liver fluke leads to obvious signs of anaemia. These are pale gums and conjunctiva (inside the eyelids); lack of stamina causing lagging or collapse when mustered; and ultimately death from lack of red blood cells needed to carry oxygen around the body.

Swelling under the jaw (bottle jaw) results from both severe barber’s pole worm and liver fluke infections. The loss of blood results in anaemia and less protein in the blood. This imbalance in the normal body fluids results in fluid accumulating under the jaw in some, but not all, affected animals. It does not always occur during an outbreak of barber’s pole worm disease, and can also be caused by other factors (e.g. a severe lack of protein in under-nourished sheep).

6. What type of environment do barber’s pole worm prefer?

Barber’s pole worm is most commonly found in Queensland and the northern half of NSW where summer rainfall is common or dominant. This worm is less of a problem in the winter rainfall areas of Australia, but localised pockets exist in all states and infections are worse in summers that are wetter than usual.

7. There are two common species of black scour worm, which one is the most pathogenic and where does it more often occur?

Black scour worms occur in all sheep production districts of Australia. Trichostrongylus colubriformis and Trichostrongylus vitrinus are the main species causing disease in Australia. Generally, T. colubriformis occurs in the warmer summer rainfall areas and T. vitrinus  occurs more frequently in winter rainfall areas.

T. vitrinus is considerably more pathogenic than T. colubriformis, meaning that it needs to be treated at lower egg counts. Regular worm egg counts are essential for successful management.

8. Should lambs be regularly treated for intestinal tapeworm?

While tapeworms are large and the segments passing in the dung are very obvious, there is no consistent evidence that they cause production loss or ill-health. Therefore, treatment for tapeworms is not warranted.

Intestinal tapeworms (Moniezia) are blamed for a range of sheep problems, but there is no hard evidence for any effects on production or health. Treating specifically for intestinal tapeworm is unlikely to be beneficial, whether in terms of scouring or weight gains. It is more important to effectively treat the less visible worms (the important sheep roundworms), which can cause severe production losses and death.