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Diagnosing parasites: What tests work best for worms??


Livestock producers have several ways to check for worms. But some tests are better than others. We put the different options under the microscope and ranked the common methods to see how they compare.

 

  1. Worm egg count (WEC)- this test is top-ranked for several reasons.
    1. Timely- signals problems before the animals get sick or lose production
    2. Cheap- pooled (bulk) tests cost in the region of $60 for a mob
    3. Available -producers can just take some faecal samples themselves and send to the lab, or submit to your local ParaBoss WEC QA-accredited vet or store
    4. Quantitative- the number of worm eggs counted gives an indication of how bad the infection is and the impact it will have on a mob. This allows economic and animal health decisions to be made on good evidence.
    5. Identify worm types- when combined with larval culture and differentiation (worm ID)
    6. Flexible- can be used to check if drenches are effective (if WEC is done 14d after the drench) or if liver fluke eggs are present (using the sedimentation test) or identify coccidiosis and tapeworm. Individual counts will show the range of counts in a mob.
    7. Linked to management- plan to collect samples before lamb-marking, weaning, pre-lamb, vaccination, crutching or shearing. Also, allows manager to change paddocks or supplementary feed based on WECs and also select rams and ewes based on how well they suppress worm numbers (ASBVs).
    8. Helps planning- knowing the worm egg count allows us to figure out how badly contaminated a paddock is and when it will be safe to graze.

 

The downside of worm egg counts is that variation in sampling methods means results reported may not reflect the real situation in the mob. Also, some people may feel uncomfortable about handling dung samples, especially when it involves taking them directly from the animal’s rectum such as for a drench test. There is also a risk of infection if good hygiene is not observed.

 

  1. Post-mortem inspection- used at the processing works to collect data on common ‘meat quality parasites’ such as hydatids, sheep measles (Taenia ovis) and bladder worm, it can also be used as a field investigation tool.  Unfortunately, by the time we get to do this test the animals are already dead.

 

The upside is that a skilled veterinarian can take samples to confirm or exclude other diseases, as well as identify worms in the gastrointestinal tract, liver, abdomen and lungs. The downside is that many of our most common and deadly parasites are either too small to see, or disappear as they are digested within the first few hours of death.

 

  1. Animal signs. Yes, the stock themselves will tell us when they are sick with worms. Depending on the type and number worms, stock will show signs such as scouring, dags on the breech or down the back legs, bottle jaw, pale colour in the eyes, mouth and vaginal mucosa, inability to exercise, going down, lack of appetite, low body condition score.

 

However, these signs only appear after the mob has already been losing weight and accumulating worms and contaminating paddocks. Also, these signs aren’t specific for worms and can be confusing to interpret.

 

  1. Regular bodyweights- can be made easier with individual electronic ID eartags and automatic drafting. This will allow decisions to be made for treatments as well as for trials, such as when half the mob is drenched and then bodyweights compared a month later. Note that a trial like this needs to be set up so that other factors such as nutrition, age, genetics, sex or prior management don’t affect (confound) the results. Helps to also use body condition score.

Figure 1: Signs of worms such as bottle jaw means that worms have already caused a lot of physical damage and loss of production to the animals in the mob (see point 3 above).

 

  1. Examination of dung- sometimes obvious worms including tapeworm segments are visible in the dung or on the ground. Although interesting, these don’t really provide information about if or when the mob needs treatment, as they don’t relate closely to worm burden or forecast a response to treatment.

Figure 2: Weighing mobs of stock on a regular basis allows managers to know if a drench or other treatment has led to better liveweight gains (see point 4 above)

 

  1. Advanced laboratory methods- these include :
    1. faecal, milk or blood ELISA for liver fluke These tests are highly repeatable and precise and allow detection of liver fluke before they lay eggs (a downside of the sedimentation test). They do require interpretation by experienced practitioners.
    2. molecular methods (PCR) to identify worm types. This technology works best when large numbers of samples are tested simultaneously. Not widely available.

 

To find out more information about diagnostic tests for worms, see:

WormBoss cattle

WormBoss sheep

List of professional providers (including WEC QA-accredited laboratories in your state)