Flock leads way on worm resistance

Headshot of Bob Garnant
Bob GarnantThe West Australian

The Rylington Merino flock is recognised as the most worm resistant sheep flock in Australia - maybe the world.

Department of Agriculture and Food senior research officer John Karlsson, one of the driving force's behind the flock's establishment 25 years ago, believes with ongoing support, the flock is earmarked for further greatness for its contribution to science.

He believes it could also lead to developments in human medicines, in particular allergy research.

The Rylington Merino flock is named after the Boyup Brook property where it was established in 1987 as a collaborative effort with producers to create a research model to achieve gastro-intestinal (sheep worms) parasite control.

"A total of 95 famers and five agricultural institutions had each donated eight mated maiden ewes to set up the flock, allowing a good genetic cross-section to demonstrate the feasibility of breeding worm-resistant sheep," Dr Karlsson said.

"The flock was challenged in a winter rainfall environment of 650mm with moderate to high worm challenge."

The flock's standout performance has been its genetic gain in worm resistance without any adverse genetic correlations with other economically important production traits.

Dr Karlsson said their flock research discovered an unfavourable genetic correlation between the estimated breeding value of worm egg count and scouring, leading to a recommendation that producers select for both low WEC and reduced diarrhoea to achieve best results in worm control.

"The relative weighting applied to each production component trait will vary according to the local parasite challenge and the time frame to achieve sustainable control," he said.

The flock was relocated to Mt Barker in 1999, under the full control of the Department of Agriculture and Food, and continued to form linkages with objectively measured sheep from around Australia by introducing outside sires, mainly using artificial insemination.

"This is creating genetic linkages across flock which in turn allows flock comparisons for a range of objectively measured traits," he said.

Dr Karlsson said from this link-up, data was submitted to Sheep Genetics from which Australian Sheep Breeding Values were calculated for each trait.

He said a look back in time helped to understand the parasitic challenges encountered in intensive farming practices.

"In the wild, some 8000 to 10,000 years ago, ancestral sheep literally walked away from parasites. Whereas, today's domesticated paddock sheep, particularly those in the higher rainfall agricultural areas, are confined to set stocking and high stocking rates face a higher challenge from parasites," he said.

Dr Karlsson said drench resistance was starting to become a real problem in the 1980s with the available broad-spectrum drenches (BZ and LV).

"In 1988 the next new active group, Macrocyclic Lactones became available and in about five years the first cases of resistance were identified to this group," he said.

He said an estimated 80 per cent of WA sheep farms had Ivermectin resistant worm populations.

Dr Karlsson said sustainable worm control was becoming an important issue to overcome the biological, economical and consumer challenges. "In spite of new active drenches coming available recently, this problem will continue if not addressed," he said.

"Of the endemic sheep diseases in Australia, worms stand out as number one at $369 million for production and treatment costs.

"In WA, dags, which are caused by worms, probably cost producers $20 million per year in preventable practises, including loss of wool value and as the main predisposing trait for breech strike."

Dr Karlsson said the sheep industry needed to adopt sustainable worm control practises based on Integrated Parasite Management principles. One component of IPM in sheep worm control should be a selection of sheep that were more resistant to worms.

"This will lead to permanent and accumulative gains and also creates a cleaner and green production system," he said.

The Rylington Merino flock has demonstrated that selection for worm resistance was highly effective.

"This flock has made significant contributions to our understanding of breeding for worm resistance and to the inheritance of worm induced diarrhoea (winter scours) in sheep," Dr Karlsson said.

He said the future of the Rylington Merino flock rested with its importance as being an irreplaceable valuable resource. Flock research, Dr Karlsson said, was stirring collaboration with local universities and overseas interests.

Rylington anniversary *

The 25th anniversary of the Rylington Merino flock will be celebrated at the Department of Agriculture and Food office in South Perth this month.

The event showcasing the flock's background and research efforts with thoughts of the future will be discussed on August 23 from 12.30pm to 4.30pm at DAFWA's theatrette.

The line-up of speakers includes John Karlsson, who will provide insight into the flock's history, assisted by Australian Wool Producer of the Year Richard Coole, who was the second chairman of the flock.

DAFWA's Johan Greeff will team up with Dr Karlsson on the subject of worm resistance and selection response and also the flock's contribution to breech strike resistance.

In a collaborative research topic, Curtin University associate professor David Groth will talk about molecular genetics of sheep while UWA research professor Shimin Liu will cover the cost of immune response's artificial challenge in pen trials.

The afternoon program is open to anyone interested, please email john.karlsson@agric.wa.gov .au.

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