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Queensland worms, flies and lice update - November 2016

Brisbane: Maxine Murphy, Veterinary Parasitologist (maxine@paraboss.com.au)

The main need in the next few weeks before Christmas, as far as worms are concerned, is to determine—by worm testing—which mobs are wormy and should be drenched in the next few weeks, and which ones can be safely left until next year.

Worm testing

Whether you WormTest through a laboratory or do your own on-farm testing, the faecal samples collected for testing need to be truly representative of the sheep in the mob otherwise the information could result in not drenching the mob when many sheep were indeed, wormy.

Using Representative mobs: Ideally each mob should be tested individually, as there are usually differences between paddocks in the favourability for worm survival, the number of worm eggs being deposited by different mobs, and the time since a drench was given.

However, if there are a number of mobs that have the same drenching history, same class of sheep and very similar paddock type (including recent level of contamination from worms) then one mob can represent two others (i.e. test one in every three similar mobs) but this still carries the risk that the result from one mob may not be indicative of the worm burdens carried by the other mobs. 

For each mob, faecal samples need to be truly representative of the worminess of individuals in the mob: We know that not all sheep in a mob carry the same worm burden because many are genetically more resistant to worms than others (this is the basis of breeding for worm resistance). The tail of any mob of sheep will carry most of the worm burden (the 80/20 rule), whereas those animals at the top of the mob will always have lower worm egg counts under the same conditions.

Samples from 20 individuals provide a more accurate indication of the worm burden across a mob than 10 samples. For larger mobs, where barber’s pole worm is a problem (as there can be a much wider variation in individual worm egg count), sampling from a higher number of animals is imperative, especially in young sheep in early spring and summer after useful rains. Standard practice used to be to collect faecal samples from the top group of sheep in any mob, and also from the wormy ‘tail’ group, perform egg counts on each of the two groups, and compare the results to gauge the range in the counts across the mob for more accurate timing of drenches. This also allows for the tail group to be split off for drenching, and perhaps pastured elsewhere to reduce the overall worm burden of the original mob.

DrenchCheck

Worm egg counting is also used to check if drenches are giving adequate kill of worms by worm egg counting before and after a drench. Worm egg counts should be reduced to less than 100 epg by the drench. Faecal samples for this activity need to be collected only from wormy sheep as it is the drench under scrutiny not the sheep.

Warning: There have been reports of M. ovis, previously called ‘ epi’ or eperythrozoon, in southern Queensland.