McMaster Counting Slides

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McMaster Worm Egg Counting Slides

Faecal Worm Egg Counts – Large Animals

McMaster counting slides are widely used for performing faecal worm egg counts (F.E.Cs). Faecal worm egg counts are performed on faeces samples mainly from large animals such as horses, sheep and cattle which normally harbour low levels of worms in their guts.

We Supply Three Types Of McMaster Counting Chambers

  • All Glass McMaster Chamber
  • Glass/Hybrid McMaster Chamber
  • Acrylic McMaster Chamber

Vetlab McMaster Counting Chambers (2-Cell Acrylic)

Vetlab McMaster counting chambers are made entirely of tough acrylic. The counting slide consists of a base slide upon which a smaller slide is fixed on top of three supports thereby forming two chambers.

On the underneath of the top slide over each chamber, a grid is printed in blue ink measuring exactly 10mm x 10mm divided by 5 vertical lines (forming 6 columns). The top slide is positioned exactly 1.5mm above the base slide so the counting area of each chamber holds 0.15 ml in volume.

More Info

For more information or to buy complete F.E.C Kits please view our Parasitology page.

F.E.C. Method & Instructions

F.E.C. Method & Instructions for Use

Vetlab McMaster Counting Method

Vetlab Worm Egg Counting Method

 Equipment Needed

  • Microscope offering x40 and x100 magnifications with a mechanical stage
  • 50ml plastic graduated measuring cylinder (Cat No. 0523)
  • Ready-made Flotation Solution S.G. 1.200 (Cat No. 6107-1. 6107-5. 6108-1. 6108-5)
  • McMaster 2 Cell Counting Slide (Cat No. Glass 6602. Acrylic 6603)
  • Plastic Transfer Pipettes (Cat No. 0670)
  • Small Plastic Bowl (Cat No.6604)
  • Tea Strainer & Teaspoon
  • Tally Counter (CatNo.1897)


  1. Pour the flotation solution into the measuring cylinder up to the 26ml mark.
  2. Add faeces until the level rises to the 30ml mark.
  3. Pour the contents into the tea strainer whilst holding over the bowl.
  4. Dip the tea strainer in and out of the bowl whilst also mixing the faeces retained in the strainer with the teaspoon.
  5. Discard faecal matter retained in the tea strainer.
  6. Mix the faecal solution in the bowl with the teaspoon and immediately aspirate into a transfer pipette.
  7. Transfer the sample to fill both chambers of the McMaster slide.
  8. Stand on the bench for at least 2 minutes and no longer than 5 minutes.
  9. Transfer the McMaster slide to the microscope stage.
  10. Using the x10 objective, focus on any corner of the first grid. (Download PDF for Diagrams)
  11. Count the worm eggs in the total area of both grids and multiply by 25 to obtain the final result in eggs per gram.

Top Tips

  1. Any worm eggs present will float to the surface of the special flotation solution and sit tight underneath the top slide of the counting chamber. In order to detect these eggs, the microscope must be focused at this level. This can be achieved by sharply focusing on the edge of an air bubble or a grid line.
  2. You can speed up the counting process by using our Acrylic McMaster slide with the x4 objective (x40 magnification). This allows you to view two columns of the grid at once. However, you need to be familiar with what the eggs look like at this lower magnification so first of all identify them with the x10 objective (x100 magnification) then switch to the x4 objective (x40 magnification). This will give you confidence, later on, to routinely scan using the x4 objective.
  3. It is very important to use a flotation solution with a specific gravity which allows the faecal material to sink and worm eggs to float. We supply flotation fluid which has been adjusted to a Specific Gravity of 1.200 which is ideal for floating most worm eggs. Do not be tempted into producing your own fluid by trying to saturate tap water with solute as Specific Gravity will vary considerably.

The number of eggs per gram can be calculated as follows:

Count the number of eggs within the grid of each chamber, ignoring those eggs outside the squares.

Multiply the total by 25 – this gives the eggs per gram of faeces (e.p.g.)

For Example

12 eggs were seen in chamber 1 and 15 eggs were seen in chamber 2

= (12 + 15= 27) x 25 = 675 e.p.g


Do not delay reading the count beyond the recommended time (see procedure: 8) as the flotation fluid may distort or destroy delicate eggs. Therefore it is advisable to only process a few samples at a time.


Clean the chamber by washing it in warm water using domestic washing-up liquid applied with a soft cloth or soft brush. Rinse in clean water.

How To Clean A McMaster Slide

Faecal Flotation Solutions

Ready-Made Faecal Flotation Solutions

Made to your Specific Requirements (Sodium Nitrate & Zinc Sulphate)

Livestock & Companion Animals

Examination of faeces from livestock and companion animals for parasite eggs and oocysts is an important diagnostic procedure in most veterinary practices and laboratories. One of the most common techniques uses the concept of floating parasite eggs to the surface of a special solution in order to be detected under the microscope.

Specific Gravity

Basically, this is achieved by increasing the density or specific gravity (S.G.) by dissolving certain salts in water. The S.G. has to be optimised in order to allow parasite eggs to float and faecal debris to sink. It is generally recognised that the S.G. of faecal flotation solutions should be within the range of 1.18 to 1.27 to detect most (but not all) ova.

Vetlab Supplies Ready-made Faecal Flotation Solution

We offer ready-made faecal flotation solution of either Sodium Nitrate or Zinc Sulphate both of S.G of 1.200. These solutions are the most popular and recommended for general use. We offer both solutions to accommodate personal choice, although we find that our Sodium Nitrate Solution has less shrinkage effect on Giardia Cysts. However, we can make solutions of different S.G. values to personal order. These solutions are ideal for use with our ‘OvaTube’ and McMaster slides.

For further information follow this link


StatSpin OvaTube – Companion Animals

Improved Accuracy without the Mess!

OvaTube is the perfect in-clinic solution for fast, easy, and accurate testing on small animals such as cats and dogs. The StatSpin OvaTube is a unique device allowing you to perform faecal parasite testing using the more accurate ‘gold standard ‘centrifugal’ flotation method. With a built-in sampling tool, the StatSpin OvaTube offers a fast clean, easy and above all, superior method of detecting ova all in one unit.

For further information follow this link


Benefits of Faecal Worm Egg Counts

  • To provide an estimate of the adult worm burden in an individual or small group of animals.
  • To detect animals shedding relatively large numbers of worm eggs in their faeces and thereby posing a threat to other animals grazing the same pasture.
  • When performed as part of a Faecal Egg Reduction Test (F.E.C.R.T) to detect the efficacy of or resistance to, the anthelmintic in use.

In general, faecal worm egg counts help vets and owners maintain their livestock in good health, provide financial benefits by avoiding unnecessary worming treatments and delay/avoid the development of anthelmintic resistance.


Additional information

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