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Beyond the Bale : December 2017
The use of Worm Egg Counts (WEC) are the gold standard to decide whether sheep require a tactical drench. They are also used to test drench efficacy and assess a sheep’s resistance to worms. But which sampling method – bulk or individual – is the most appropriate? ParaBoss Operations Manager Deb Maxwell collecting a bulk sample. When it comes to tactical drench decisions, both bulk and individual sampling is better than not testing, but each method suits specific situations. Worm tests for monitoring the worm status of a mob are best done with bulks, whereas DrenchTests, DrenchChecks and WEC ASBV samples should be done individually. Where strategic drenches are given, such as a weaning, pre-lambing or first summer drench, no prior worm egg count is required. ABOUT WORM EGG COUNTS Worm egg counts are also called WEC, WormTests or faecal egg counts. They identify the number of worm eggs in faeces, on an eggs per gram (epg) basis, which is a good indication of the worm burden of sheep. Some laboratories can also perform a larval culture (also called a larval differentiation) to identify the types of worms present and their proportion. This is useful in some regions to decide the ideal drench to use based on the proportion of each worm species present. HOW DO INDIVIDUAL AND BULK SAMPLES DIFFER? When collecting dung samples from a mob, they can be collected individually or bulked together. Individual samples can be taken directly from the rectum of each sheep and placed into an individual container or bag. This method allows the sample to be associated with an individually identified sheep. About 10 adult sized dung pellets (or the equivalent amount if it is runnier) should be collected from each individual. Individual samples can also be collected from the ground in the paddock, but they must be fresh. When a mob is held for a few minutes and then allowed to slowly walk away there should be numerous individual piles of dung left. About 10 dung pellets from any one pile are put into their own container or bag and are not mixed with dung from other piles. Bulk sampling of a mob is also done in the paddock. A smaller amount is collected from each pile – three pellets – but they are placed into one larger container or bag along with the samples from other dung piles. To give a better estimate of the true average worm egg count of a mob, at least 20 piles should be sampled; increase this to 40 piles for mobs of more than 400 sheep or in barber’s pole worm areas. When only 10 individuals are sampled, the average result is less accurate, increasing the chance that an incorrect drenching decision will be made than if a larger number of animals were sampled. WHEN SHOULD INDIVIDUAL SAMPLING BE USED? The individual method must be used for DrenchTests, post-treatment Drench Checks and for determining Australian Sheep Breeding Values (ASBVs). For DrenchTests, the individual sheep need to be identified to a drench group. For a post-drenching DrenchCheck, the samples must be individually collected, but the sheep identity is not important. In both of these situations, it is important to be able to see the variation between individuals and whether any sheep may have been mis-drenched, which shows as a much higher worm egg count than the others in the group. Conversely, to calculate WEC ASBV for individual sheep, each sample must be linked to an individually identified animal. 42 ON FARM
In the Shops - March 2018