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8 May 2019 Andrew Dowling

Badly behaving ewes

This is a reminder that all may not be what it seems, and the thief may not be the guy with the mask. The following is based on a true story. 

A farming family were concerned that  triple combination resistant worms were causing problems on their high-performing lowland sheep property, with different brands of triple combination drenches seeming to be more or less effective. Drenching practice seemed tobe good with a sample of lambs being weighed and drench gun accuracy checked, however post-drench faecal samples had parasite eggs present.

A Faecal Egg Count Reduction Test (FECRT)was carried out. The great news for the farmer was that the parasite worms on the farm were highly susceptible to the drenches. The good news for the drench manufacturers was that all three triple combination orals used worked very well. We now had drench susceptible worms and a confused farmer; why had the drench appeared to be failing? What to do next involved a cup of tea, scones and a good talk about what was happening on the farm. On reflection they thought that the sheep performance wasn’t as good as it could be. Faecal samples collected from the ewes showed significant worm burden after weaning from January right throughtill March (317 to 361 eggs per gram (epg)). So it appeared that instead of the ewes reducing the number of parasite larva on the farm, they were adding to the population.

When the lambs are given an effective drench, eggs do not appear in the faeces until at least 21 days later whereas these ewes are passing parasite eggs every day and in huge numbers. A ewe with an egg count of 361 epg produces more than 3,610,000 parasite eggs every day. On this farm the ewes had become parasite contaminators. This could have been a result of their immune system being unable to manage the worm burden (genetic factors), a poorly functioning immune system (stressed,  mineral deficiency) or excessive parasite pasture larval challenge due to ineffective worm control in the lambs overwhelming the ewes’ immune systems. 

Mineral levels and ewe body condition can be monitored and remedied. Faecal egg count monitoring can be undertaken to ensure that lamb drenching is effective and allow the ewes to manage their worm population without the need to drench. If faecal egg counts indicate that the worm burden in the ewes is high again, then drenching with a capsule or an effective oral triple combination maybe  beneficial.

A study on the farm was set up to compare triple oral drench at monthly intervals. Centramax capsules were given to lambs, this was compared to a group of lambs given no treatment. Centramax capsules were also given to ewes, this was compared to a group of ewes given no treatment. Both groups of lambs grew at comparable rates. The capsuled ewes were two kilograms heavier than the undrenched ones, so removing the parasite was clearly beneficial. Even when the capsule had run its course, the worm burden of the ewes stayed undetectable. The problem was worms all along,but not for the reasons the farmer  suspected. Effective worm control is the answer here and this relies on the use of triple combination oral drenches, refugia management and the option to use Centramax capsules where they are needed.

If you suspect worms are impacting your performance on-farm, discuss your situation with your local PGG Wrightson Technical Field Representative who will be able to  offer some recommendations.


Andrew Dowling

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