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Questions

1. Name two roundworms that produce large numbers of eggs each day.

2. What age group of sheep and goats typically exhibit hypersensitivity scours in winter and spring?

3. In your region, which three months of the year would you mark on your calendar as moderate to high risk for breech and body strike? 

4. Why does shearing significantly reduce louse numbers on sheep and goats?


Figure 1. Barber's pole worms produce thousands of eggs per day. The white reproductivve tract is twisted around the pink gastrointestinal tract to give the classic "barber's pole" pattern in the females. Males are  more pink—there are two of them on the left about half way up the image. Source: Deb Maxwell

Answers

1. Name two roundworms that produce large numbers of eggs each day.

The adult female large bowel worm and nodule worm lay about 5000–12000 eggs per day, the barber’s pole adult female between 5000 and 10000 eggs per day, and the large-mouthed bowel worm about 5000 eggs per day. 

By contrast, the brown stomach worm produces only about 50–100 eggs per day.

Different roundworms have different egg-producing capacities and it is thought that the eggs of those worms that do produce large numbers of the eggs each day, are not well adapted to less than optimal environmental conditions, and that blanketing the environment with eggs will ensure the survival of at least some.  

The eggs of the brown stomach worms have, for example adapted to adverse environmental conditions, and can suspend hatching for a number of months when necessary. With this adaptation, fewer eggs are required to ensure the survival of this worm.

 

2.  What age group of sheep and goats typically exhibit hypersensitivity scours in winter and spring?

Hypersensitivity scours typically occurs in animals that have developed their adult worm immunity i.e. mature animals, and occurs in response to ingestion of scour worm larvae.

It is an allergic reaction manifest by the gut and is different from the normal scour worm infestation that typically occurs in all age groups and mostly in response to adult worms.

The course of disease in goats follows that seen in sheep.

Scouring, whether due to large burdens of worms or a hypersensitivity reaction, results in the wool or hair near the breech becoming coated with lumps of faeces (dags), which in sheep increases their susceptibility to flystrike.

 

3.  In your region, which three months of the year would you mark on your calendar as moderate to high risk for breech and body strike? 

The risk of flystrike increases once the temperature is above 17°C and when wind speeds are moderate (<30 km per hour). In general, the summer months are a greater risk time than the winter months. Rainfall and overcast weather that can result in the fleece remaining moist also increase the risk of strike.  

The FlyBoss tools allow you to assess flystrike risk using your weather and climate details. The graphs have been generated for two typical sheep environments – one summer rainfall and one winter rainfall.

 

4.  Why does shearing significantly reduce louse numbers on sheep and goats?

Biting lice do not like being exposed to light and actively move away from it.

When sheep, and goats bred for their fleece, are in full sunlight in the paddock, lice are typically found deep in the fleece close to the skin. However, when animals are in the shearing shed and the fleece is shaded, lice move higher up into the fleece and especially in response to shearing when the skin area is exposed to light.  

About sixty to eighty percent of lice are removed directly with the fleece by shearing.

Any remaining lice are usually found in poorly shorn patches, but once stock are returned to the paddock many (but not all) of these lice are killed by high temperatures and strong sunlight.

Sheep biting lice are different from the ones carried by goats and do not breed on goats, and vice versa.