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Almost all sheep have internal parasites. They often don’t cause any disease and sheep can look normal or even fantastic. However if worms get out of control, sheep can suffer from both subclinical disease (no outward signs) or clinical disease (signs range from very subtle to obvious, including death).
Usually after weight loss, blood loss, anaemia or from fly strike
Reduced wool production
Reduced meat production
Decreased reproductive performance
Table 1: Effects of worms on production of sheep
A sheep with a zero worm burden has no comprise to its production, wool, lamb or meat as a result. There is an impact on production from the lowest worm burden through reduced appetite, refocus of immune system to the parasite, damage to the gastrointestinal system and potential blood loss. The visual effects (clinical signs) are apparent when the worm burden becomes high and there is substantial reduction in production and a negative impact on the health of the animal. It is the non-visual (sub-clinical) effects which accounts for the majority of production loss in a sheep enterprise as it can occur unknown over a long time frame.
The diagnostic tools
Faecal Egg Counts (FECs) also known as Worm Egg Counts (WEC)
Larval Cultures (speciate the worm eggs – for example barbers pole or black scour worm)
Worm Egg counts and larval cultures can give valuable information on existing (adult) worm burdens and paddock larval populations if samples are taken just before drenching, and on drench efficacy if faecal samples are taken 10-14 days after drenching.
How to conduct a drench check and Drench Test
‘Before and After’ FEC Testing
Carrying out FEC Reduction Tests on your property in the past has created a lot of work for everyone involved. Moreover, using traditional methods the untreated control group may have a very low worm egg count, making the treated groups results not even a reliable indication of the drench resistance status on the property.
To this end, a new test was developed which uses ‘before and after’ testing on a routine drench. This means only testing one product/drench and collecting random samples from the mob instead of particular individual animals. This way at every drench (potentially several times a year) an additional source of information on the drench performance is gathered.
Traditional Drench Test or FECRT
The traditional way to assess drench efficacy is using a drench resistance test or Faecal Egg Count Reduction Test (FECRT), also known as Worm Egg Count Reduction Test (WECRT). You should contact your local veterinarian, sheep consultant or Department sheep officer when planning this test to ensure that the work involved yields the most useful results possible. They will give good advice on mob and drench selection for the test and other local requirements such as the number of animals and faecal sample collection techniques that are necessary.
A drench resistance test is best carried out on a group of wormy, young, undrenched sheep such as lambs approaching weaning age. An initial worm egg count of the selected sheep is important before the main test is started to check that sufficient worms of the necessary species are present to make the test worthwhile. An average worm egg count of at least 300 eggs per gram (epg) is the general rule. Once a suitable mob of test animals has been found they are randomly drafted in to groups of 15 animals.
One group is randomly allocated to each of the drench groups to be tested and an additional group is needed to provide untreated control animals. Sheep should be adequately identified to their groups and then receive an individual dose of their respective products. This is carefully calculated and checked on the heaviest individual within each group. Sheep in the control group remain untreated. After treatment, all of the sheep can be run together or as part of any other mob of sheep until it is time for post-treatment sampling.
At 14 days after treatment (this timing is critical for a good result) the sheep should be re-mustered and individual faecal samples collected from each group, including the controls. Individual worm egg counts for each sampled sheep and a bulk larval culture for each group should be carried out using the collected samples.
1. Meat and Livestock Australia. Priority list of endemic diseases for the red meat industries. Published March 2015. Project code B.AHE.0010.
Sheep Internal Parasites & Best Practice Worm Monitoring