As a veterinarian, you already know that parasitic, intestinal worms can cause diseases in pretty much all species we treat - large and small. In recent years, many of these worms have developed resistance to the chemical wormers commonly used. Most commonly noted in horses and production animal species, however, the emergence of this resistance in companion animals should not be overlooked. 

As an example, about 80% of horses receive regular worming treatments while just 20-30% of these actually have the parasites - this increases the rate of resistance development in worms. This is where Fecal Worm Egg Counts (FWECs) come into play to monitor the efficacy of particular treatment plans, medications and determine which animals actually need the worming treatment.

One of the great things about FWEC tests are that there's minimal need for specialized equipment needed, just a microscope and some time. Every practice has a compound microscope for viewing blood smears etc and the same one can be used for FWEC in a pinch. In an ideal world, separate parasitology and clinical pathology microscopes would be available as the salt solutions for performing FWEC microscopy can tarnish a scope.

Why do FWECs and relative expense

Why should we, as vets, go to the hassle and expense of performing these FWECs? It’s our responsibility to use appropriate treatments and at the appropriate intervals and this doesn’t just include judicious use of antibiotics.

It’s important to remember that FWEC’s are a ratio (eggs per gram of faeces) and may not be a reliable indicator of the cost of a parasite to their host. There are a significant number of resilient animals that continue to meet performance targets in spite of high FWECs. Having said this, FWECs can provide a useful indication of a nematode infection and may be more useful in poor performing individuals within the herd rather than whole herd deworming on the basis of pooled FWECs.

*FWECs only quantify adult worms that lay eggs within the lifecycle. This test doesn’t identify immature larvae, encysted cyathostomins (encysted small redworm), tapeworms, bots nor tapeworms.

Reasons to consider FWECRTs

Fecal worm egg count reduction tests (FWECRTs) are a good option for flocks/herds investigating the efficacy of their anthelmintic treatments or relative resistance within a population. Using these tests in conjunction with a targeted treatment regimen helps to reduce the selection pressure on parasites to develop resistance, reduce the costs of anthelmintic treatments for clients and arguably reduce the incidence of certain clinical diseases, such as those seen in equids.

Techniques

There are a number of techniques for obtaining FWECs for a variety of animal species.

Arguably the most common and efficient one of these is a flotation test called the Modified McMaster Test. The goal is to separate eggs from fecal debris where the eggs will float to the surface of a counting chamber for ease of enumeration under the microscope.

Other methods include the Cornell-Wisconsin and FLOTAC techniques.

There are some great videos and instruction outlines available online to help perform FWECs, check out our preferences here and here.

Note: Technique consistency is most important for performing these tests.

Equipment and Consumables

As the Modified McMaster Test is widely used, we’re going to list the typical consumables required to perform this test. This test is suitable to determine the concentration of strongyle and Haemonchus contortus eggs.

• Scales in 0.1g increments
• Two cups that hold a minimum of 5 oz.
• Flotation solution (saturated sugar or salt solution, commercial product or “homemade”)
• Syringe to measure flotation solution
• Spoon to stir
• Gauze to strain the fluid
• 2-chamber McMaster slide
• Pipette to fill the slide
• Compound microscope
• Stopwatch

We sell our own Faecal Egg Count Kit shown below:

Microscope

Specs required

At a minimum you should use a compound microscope that has an internal light source and moveable stage. These microscopes generally have multiple objective lenses, for FWECs you’ll use both the 4X and 10X lenses. A monocular microscope is sufficient, but a binocular is much more comfortable to use.

We recommend the Optico XSZ-107B Binocular Microscope

Check out our FWEC bundle that includes this microscope on our site here. This bundle includes everything you need to perform the McMaster technique.

The Optico XSZ-107B is an advanced binocular microscope designed for modern veterinary practice laboratories. With optics matching larger professional scopes,  this microscope is reliable, accurate and long-lasting. The Optico XSZ-107B’s binocular head is inclined at a comfortable 45^o  with a wide-field eyepiece to meet your ergonomic needs. 

Adjustable brightness with an Abbe NA1.25 condenser, iris and spiral reduces eye strain while maximizing your visibility when performing the McMaster technique. 

McMaster Slide

McMaster Slide for Fecal Egg Count or Worm Egg Counting
The printed grids are bonded to the surface of the underside of the slide; they will not come off or wear with use. Simply rinse the slide thoroughly under warm running water and re-use again and again. With proper care the slides will last indefinitely.

Conclusion

FWECs are an important diagnostic tool that you can offer your clients with relatively inexpensive equipment that can have multiple uses within your practice laboratory. More likely to be used in production animal or equine species, they can also be helpful for companion animal parasitic investigations. Our recommended microscope is the Optico XSZ-107B which is available alone or within the FWEC bundle and is sure to meet your practice’s microscopy needs.

References

Von Samson-Himmelstjerna, G., R.C.A. Thompson, J. Krücken, W. Grant, D.D. Bowman, M. Schnyder & P. Deplazes (2021). Spread of anthelmintic resistance in intestinal helminths of dogs and cats is currently less pronounced than in ruminants and horses - Yet it is of major concern. Int. J. Parasitol - Drug 17 pp36-45

Wolstenholme, A.J., C.C. Evans, P.D. Jimenez & A.R. Moorhead (2015). The emergence of macrocyclic lactone resistance in the canine heartworm, Dirofilaria immitis. Parasitology 142(10) pp1249-1259

Neilsen M.K. (2012). Sustainable equine parasite control: Perspectives and research needs. Vet. Parasitol. 185(1) pp32-44

Lester, H.E., D.J. Bartley, E.R. Morgan, J.E. Hodgkinson, C.H. Stratford & J.B. Matthews (2013). A cost comparison of faecal egg count-directed anthelmintic delivery versus interval programme treatments in horses. Vet. Rec. 173(15) p371

Greer, A.W. & A.R. Sykes (2012). Are faecal egg counts approaching their “sell-by” date? Proc. NZSAP 72 pp199-204

Web.uri.edu. 2021. [online] Available at: <https://web.uri.edu/sheepngoat/files/McMaster-Test_Final3.pdf> [Accessed 24 October 2021].

FEC SOURCE. 2021. MCMASTER TESTING METHODS — FEC SOURCE. [online] Available at: <https://www.fecsource.com/mcmaster-testing-methods> [Accessed 24 October 2021].