Lifting the limits imposed by worms on sheep meat production

Summary

The impact of gastrointestinal nematode parasites (worms) represents the highest animal health cost to the Australian sheep industry but surprisingly little attention has been paid to worm control in sheep meat systems.

The primary objective of the work conducted during this project was to develop and evaluate integrated worm control programs for meat sheep systems in four geographical regions of eastern Australia.

The main feature to emerge from this project was identification that integrated worm control programs can almost completely remove the deleterious effects of worm infection and have benefit for drench resistance and therefore sustainability of worm control.

Objectives

The project aimed to develop integrated worm control programs that lift the limits imposed by worm infection for sheep meat systems, and ensure the adoption of these programs by a significant number of advisors and their clients.

Key findings

The conclusions from project activity were:
• Adoption of integrated Lifting the Limits (LTL) worm control resulted in lower worm egg count and was achieved with fewer treatments and less reliance on long-acting products with benefits most pronounced where Barber’s Pole worm was dominant. These changes should reduce selection pressure for drench resistance.
• Both LTL and typical worm control provided protection that was almost as good as year-long worm suppression, highlighting the effectiveness of management programs.
• Meat-breeds and crossbred genotypes in good condition and grazing improved pastures were very resilient to the impacts of worms with little effect on ewe and lamb live weight, fleece weight, reproduction and mortality.
• When lamb growth exceeded 200 g/day there was no benefit for weaning weight from drenches given to lambs before weaning.
• Apparent mortality (though unaffected by worm infection) of twin-bearing ewes was in the range 3.9–10.2% p.a., surpassing accepted benchmarks. Where cause of death was established, dystocia was the main cause.
• By itself, worm egg count (WEC) was not a reliable indicator of production loss but is useful as a means of managing pasture infectivity and, in summer rainfall regions, for avoiding mortality.

Benefits to industry

Improved worm control programs can deliver the following benefits:
• Improved animal welfare with reduced worm-related adult mortality.
• Increased sheep meat production as a result of reduced parasitism and mortality.
• Elimination of unnecessary drench treatments leading to a reduction in drench treatment frequency and reduced selection pressure for development of drench resistance.
• Increased annual gross margin returns

MLA action

The project findings should be incorporated into WormBoss to provide information specific for prime lamb production. This may mean modification of programs, decision guides and other information. Each partner organisation will address producer groups directly or through the media to inform of the key recommendations. In addition to these actions, MLA should take responsibility for the transfer of key conclusions into extension materials aimed at advisors and producers.

Future research

There were a number of research opportunities identified throughout the project and these are detailed within the report. Minimising the exposure of lambs to infective worm stages after weaning is identified as an important issue for post weaning growth across regions. Mitigating this effect, without recourse to blanket anthelmintic treatment, will require weaners to graze low worm-risk pastures. Further research is required to adapt smart grazing methods for use in prime lamb enterprises in southern and northern regions.