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Just how resilient are prime lambs to worm infection?

by Lewis Kahn, ParaBoss Executive Officer

July 2016


We all know the difficulties that Merino lambs face from worm infection, but meat-breed (often XB) lambs might be a different matter. The Lifting the Limits project, supported by Meat & Livestock Australia, investigated the constraints imposed by worm infection for sheep meat systems, and worked with regional advisory groups to develop and promote worm control programs that will become available through WormBoss. 

This work showed that prime lambs that have high growth rates before weaning are very resilient to worms and are not likely to benefit from a drench before weaning.

In total, some 10,000 meat-breed ewes and their (largely) twin lambs were monitored for worm and production traits across 3 years on commercial sheep properties spread across the Northern Tablelands, Central Tablelands and South West Slopes of NSW and Victoria.

To identify the production loss caused by worms, half of the ewes received treatments to suppress worms throughout the year, which were a mixture of effective short and long-acting treatments.  The other half received treatments only as required.  The same approach was taken with the lambs from marking, when half of the lambs were treated to suppress worms and the remaining received no worm treatment before weaning.

Lamb worm egg count and live weight

The lambs grew at over 200 g/day from marking to weaning and there was no advantage from treatment to suppress worms in the lambs.  This occurred across all regions and indicates the lambs were completely resilient to worm infection.

Within the Northern Tablelands, lambs that remained untreated had a worm egg count of 1700 epg by weaning, as compared to 190 epg for worm suppressed lambs.  The infection was predominately (70%) from barber’s pole worm with scour worms making up the remaining 30% from culture.  Clearly these lambs were not resistant to worm infection.

The question remaining to be answered was if the lambs were resilient to infection.  By weaning, the untreated lambs weighed 31.9 kg and worm suppressed lambs, 32.2 kg; a difference which was not statistically different.  Clearly these lambs were highly resilient to worm infection.

Figure 1. Worm egg count of lambs at 1 and 3 months after lambing
Figure 1. Worm egg count of lambs at 1 and 3 months after lambing
Figure 2. Live weight of lambs at 1 and 3 months after lambing
Figure 2. Live weight of lambs at 1 and 3 months after lambing

Take home message

Managing nutrition to ensure that lambs grow rapidly (at least 200 g/day) until weaning is a powerful means of increasing their resilience to worms and avoiding unnecessary treatments.