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ARTICLES >> Livestock Articles

Reducing the Flystrike Risk

Posted by Bestprac on Mar 01 2012

By Liz Guerin
Flystrike costs the sheep industry around $280 million per year in the form of lost productivity, mortality and costs of control. Recent high rainfall and warm conditions across Australia have meant optimal fly conditions and whilst productivity loss has been the result for many sheep producers, there have also been flocks that have ‘survived’ these wet seasons with very low levels of strike.

Key messages:

  • There are simple steps producers can take to reduce the risk and incidence of flystrike in flocks
  • Strategic use of shearing, crutching and chemicals can be used to further reduce flystrike risk
  • Using breeding values and balanced breeding objectives we can select animals that have good fleece weight and also are plain and flystrike resistant
  • For further information go to the FlyBoss website www.flyboss.org.au  

Lu Hogan of the Sheep CRC says that producers need to adopt the best integrated solution for flystrike management that suits their business, their environment and the type of sheep they run, and in most cases this will be an individual solution.

There are simple steps producers can take to reduce the risk and incidence of flystrike in flocks with advantages including increased productivity in terms of more lambs and more wool and reduced mortality.

“The first step is to understand the traits and factors that make sheep susceptible to flystrike. This will help producers assess their flocks and the risk scale for those animals, then selection policies and breeding can be put in place to reduce that risk over time,” she said. “Strategic use of shearing, crutching and chemicals can be used, to further reduce risk, and mulesing practices need to be considered. Lastly, it all needs to be put into a flystrike management plan.”

The susceptibility of sheep to flystrike is described using a set of industry developed scores for the key visual traits including wrinkle, fleece rot and dags. The scoring system works on a range of 1 to 5, with score 1 animals showing no evidence of the trait, up to a score of 5 with the animal showing the trait most strongly.

Research conducted at Armidale, NSW over the last 5 years, showed that as wrinkle scores increase from 1 to 5 there was a dramatic increase in incidence of flystrike.

“If wrinkle score can be kept down to 1 or 2, the impact of breech strike can be kept at a manageable level and the time of shearing and crutching and chemicals can keep control of flystrike” Ms Hogan said. “But in a flock with scores around 3, 4 or 5 there are real issues with managing the incidence of breech strike.”

Despite this recent research, Ms Hogan says that the same data was available in 1940, with producers being warned not to rely on mulesing operations alone, and that breeding plainer sheep should be an objective.

“We knew in 1940 that wrinkly sheep suffered more breech strike. The data from the NSW study showed that unmulesed, wrinkly animals had flystrike rates between 30 and 100% whilst unmulesed, plain breeched animals had flystrike rates between 10 and 20%,” Ms Hogan said. “Had these plain breeched animals also been mulesed, the incidence of strike was reduced down to less than 5%.”

Randomly sampling a mob and wrinkle scoring them will give producers an idea of their average wrinkle scores and their distribution.

“The average score will give an indication of the breech strike risk faced and whether higher risk animals can realistically be classed out whilst still having a reasonable number of replacements,” Ms Hogan said.

Fleece rot is another important trait which contributes to the risk of body strike. Factors contributing to fleece rot include structural conformation of the animal, fleece structure, skin type and wool quality characteristics. Score 1 animals have no evidence of colour or staining in the wool; scores 2 and 3 have an amount of bacterial staining or colouring in the wool with scores 4 and 5 have a visible ‘crustiness’ caused by exudates from the sheep’s skin. It is these animals are quite susceptible to body strike.

“In rangeland environments this may not be seen frequently and so applying selection pressure to this trait is difficult,” Ms Hogan said. “However, even in a dry year, where fleece rot score 4 or 5 animals in the flock may not be evident, applying some pressure to score 2 or 3 animals can decrease fleece rot risk as these are the ones that will turn into score 4 or 5 in wet year.”

Dags also make sheep susceptible to flystrike with score 4 animals being 7 times more likely to be struck in the breech than a score 1 animal. Eliminating these animals will reduce the amount of dag present in a rangelands environment.

Generally speaking, achieving a flock with average scores of 1 or 2 as soon as possible will reduce the risk of flystrike.

“We need to stop breeding replacements from high wrinkle score sheep and either cull them if there are only a few, or if there are more, use them to breed your first cross or prime lambs,” Ms Hogan said. “Applying consistent selection pressure every year will reduce the flystrike risk when the wet years do occur.”

Ms Hogan said that a lot of people think that selecting plainer animals to reduce flystrike risk will result in loss of fleece weight.

“By using breeding values and balanced breeding objectives we can still select animals that have good fleece weight and also are plain and flystrike resistant,” she said.

Ms Hogan says that by examining a range of sires in the MerinoSelect database for their wrinkle traits, significant change could be achieved in one cross by bringing in external genetics to flocks.

“There are plenty of sires with low breech wrinkle and good clean fleece weight and these are the sires growers need to be looking for in order to make rapid gains.”

Reducing body wrinkle can be achieved even quicker by putting selection pressure on both the ewes and the rams at the same time.

The other management tools of selecting the best shearing and crutching times and applying chemicals appropriately will provide added protection to the flock. Flyboss, a CD based planning tool, uses weather data and scientific research on risk to help optimise shearing and crutching times and chemical treatments into a management plan for the property.

“Your own data on joining, lambing, shearing and crutching times in addition to body wrinkle and breech cover scores, are put into the model. The region and climatic conditions will then give you a plot of the relative risk of flystrike throughout the year,” Ms Hogan said.

Scenarios where shearing and crutching times are changed in combination with the use of chemicals and mulesing can be applied to determine how best to lower flystrike risk for your conditions and situation.

“It is a great tool to help growers in their planning and work out what is important in their business and how they can best manage their flystrike risk,” Ms Hogan said.

For further information please go to the FlyBoss website www.flyboss.org.au

Last changed: Mar 02 2012

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