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1. Under what conditions would you consider using a long-acting drench for worm control?
2. What management strategies are considered appropriate for purchased sheep in the period after the quarantine drench?
3. What causes fleece rot, and why is it important?
4. When purchasing sheep, what factors about the place of origin or the sheep themselves, would increase the risk of lousy sheep?
Long-acting drenches are ideal for use where paddock infective larval burdens are high, or where immunity levels to worms could be low (e.g. lactating ewes and Merino weaners).
The frequent significant rain events, and extensive flooding currently being experienced across many sheep areas, could isolate and restrict sheep and goat movements for 6 or more weeks. Under these conditions, a long-acting drench will provide significant protection against the increased levels of larval pick-up.
When stock is confined at increased stocking rates, worm burdens rapidly increase as the disease is easily transmitted between animals.
Effective persistent or long-acting treatments kill immature and adult worms at the time of treatment. They also kill any infective larvae eaten by animals (with pasture) during the period of protection of the treatment—for sheep, this is about 3 months for long-acting and 1–6 weeks for mid-length treatments (depending on the particular product).
*Be aware that use of persistent products can accelarate development of drench resistance (as it is like giving the same drench each day for 3 months), and that resistance of barber's pole worms to moxidectin (in the long acting injectable products) is already common. Where possible, use all worm control strategies rather than relying on persistent products.
Sheep should be managed in a holding paddock with access to feed and water, ideally for 4 days after drenching. Although the drench will have killed the worms—providing you have used an effective drench—it won’t have killed all the worm eggs still in the sheep and the 4 days are required for the remaining worm eggs to pass out of the sheep.
Don't use the contaminated holding paddocks again for at least 2–5 months. The shortest period of 2 months is for hot regions in summer when the daily maximum temperatures are 30°C or more, and the longest period is for cool areas in winter, when temperatures are 15°C or less. This rest period provides any resistant infective larvae hatched from eggs time to die.
If you purchase more sheep and quarantine drench them, you won’t be able to use the same holding paddocks if it is within the 2–5 months of their first use, as the sheep can become re-infected with resistant larvae from the first group of sheep.
If you are bringing multiple mobs in over time, the best option is to feed and water them in a yard for the few days. The bare dirt is not favourable for worm larvae to develop and re-infect other sheep, and so avoids the problems of managing the holding paddocks.
Yarding and feeding for the few days involves a change of mindset—look upon the small extra cost and workload as insurance and just a part of "buying expenses", like commission and freight. It also provides the extra benefits of improved initial monitoring for ill-health or lice and allows the majority of any undesirable weed seeds in the sheep to also pass out into a controlled environment.
Fleece rot is due to moisture (usually present for about 5 to 7 days) and bacterial overgrowth developing at the skin level of sheep. Wetting down to the skin level and the subsequent time before the skin dries are the two key risk factors.
Some sheep are more prone to fleece rot than others, generally through a variety of genetic factors including wool colour and the amount of sweat (suint) versus wax, wool staple and tip structure, and conformation of the backline of the sheep.
Water has an emulsifying effect on the wool wax layer leading to damage of the protective barrier at the skin. Wetting unprotected skin leads to inflammatory skin lesions such as maceration and micro abscess formation in the outer skin layer and leakage of serous fluid.
The term, fleece rot, refers to the wool discolouration and crusted banding across the wool fibres and parallel to the skin. Discoloured bands can be yellow, green, red-orange, pink-violet, blue, brown or grey.
The Visual Sheep Scores Guide, Version 2–2013 provides a common industry language for describing and assessing fleece rot in sheep.
The presence of fleece rot is a predisposing factor for body strike. The higher the score, the more severe the fleece rot and hence the risk of body strike in the sheep. Therefore, the risk of body strike is reduced by reducing the incidence of fleece rot in the flock.
There is an increased risk of lice if sheep are bought from a high-risk source property that has one or more of the following:
The sheep themselves are high-risk introductions if:
It takes at least 3 months from the time of the initial infestation for 'rubbing', an indicator of the presence of lice to become apparent. Sometimes lice, eventhough present, may not be able to be seen for up to 6 months.