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Questions

1.   Why do dual- and multi-active drenches better protect against drench resistance than single-active drenches?

2.   How does tail docking reduce the risk of flystrike in lambs?

3.   If the most important liver fluke drench is given in April when should the second most important liver fluke drench be given and why?

 4.  If lice are found in long wool, how would you determine if a long wool treatment is necessary before shearing?


Tail docking reduces the risk of flystrike in lambs.
Tail docking reduces the risk of flystrike in lambs.

 

Answers

1. Why do dual- and multi-active drenches better protect against drench resistance than single-active drenches?

Each drench group (ingredient, active) works in a different way to kill worms. A worm that is resistant to a drench carries “resistance genes” that are particular to that drench and enables it to survive (resist) the drench treatment. However, different drench groups are subject to different sets of resistant genes. 

Therefore, the chance of a worm having multiple sets of resistant genes is much lower than having genes resistant to just one drench group. So, dual- and multi-active drenches have a greater capacity to kill closer to 100% of the worm burden than a single-active drench, particularly when drench resistance is widespread.

The overall effect is slower development of drench resistance

2. How does tail docking reduce the risk of flystrike in lambs?

Docking the tail at the correct length enables lambs to control their ability to direct faeces and urine away from the body to prevent soiling their hindquarters. Soiling in the breech area attracts blowflies.

Research over many years has shown that the two most important risk factors for breech strike are dags (the result of scour worm burdens), and wrinkle of the skin in the breech area and breech cover is the next most important trait as it can exacerbate the effect of wrinkles and dags, particularly when these are at lower scores.

3.   If the most important liver fluke drench is given in April when should the second most important liver fluke drench be given and why?

The second most important liver fluke drench is usually given in August to September.

Even when a highly effective flukicide (one based on triclabendazole) is used at the April/ May drench sheep and goats may still be flukey in August because even the best flukicides do not kill every single fluke. Any young fluke (harder to kill) left behind at the April/May drench will be an adult by spring and living in the bile ducts and producing eggs.

The two other reasons sheep may have some fluke coming into spring is that they picked up some metacercariae from the pastures over winter, and perhaps fluke were resistant to the flukicide used in autumn.

4. If lice are found in long wool, how would you determine if a long wool treatment is necessary before shearing?

The long wool treatment tool will help you determine if this treatment will be necessary and cost-effective. Its calculations are based on the current level of wool damage in the mob to estimate the additional damage that might occur from lice if sheep are not treated before shearing. The costs of treatment are compared to the estimated costs of wool damage to determine if a treatment will be cost-effective.

It is important to note that long wool treatments do not remove lice. Sheep treated before shearing will also need treatment after shearing unless the infestation was low enough to be mostly removed by shearing.