McMaster Counting Slides
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McMaster Counting Slides

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.C’s). 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.

Vetlab McMaster Counting Slides (2-Cell Acrylic)

Vetlab McMaster counting slides 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.

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Vetlab McMaster counting slides have some significant advantages compared to the conventional glass type

  • The counting slides are made from the strongest optical acrylic available — therefore, are more robust than glass.
  • The upper section is fused to the lower section by sonic welding rather than glue. This makes the slide more durable and as a result, avoids faecal residue being trapped between the pieces.
  • The 6 grid columns making counting faster as their width exactly match the width of field of view of the microscope at x40 and x100 magnification.
  • The upper section grids are printed in blue ink which lasts for some years with correct care. This allows the grid lines to be focused on more easily and worm eggs to be seen clearly underneath the grid lines.
  • Our Vetlab McMaster counting slides are less than one-third of the cost of a conventional glass slide, therefore making them exceptional value for money.

Marienfeld McMaster Counting Slides (2-Cell Glass)

Marienfeld counting slides are an almost identical design to our own Vetlab counting slide however, they are made of glass and the top slide and supports are glued together.

The counting area grids are etched into the glass (rather than printed) and the grid area is divided into 10 columns (rather than 6 columns). The counting volume is identical to the Vetlab counting slide.

F.E.C. Method & Instructions for Use

Vetlab Worm Egg Counting Method

 Equipment Needed

  • Microscope offering x40 and x100 magnifications, and 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


  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 faeces retained in the strainer with the teaspoon.
  5. Discard faecal matter retained in the tea strainer.
  6. Mix 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 seen in chamber 1 and 15 eggs seen in chamber 2

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


Do not delay reading the count beyond 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.


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 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 built-in sampling tool the StatSpin OvaTube offers a fast clean, easy and above all, a 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.


Cat NoDescriptionPrice
6602Marienfeld Superior, McMaster Counting Slide, 2 Cell, Glass £119.00 (ex VAT)
6603Vetlab McMaster Counting Slide, 2 Cell, Acrylic £39.50 (ex VAT)
6107-1Sodium Nitrate Solution 1 Litre SG 1.200 £12.00 (ex VAT)
6107-5Sodium Nitrate Solution 5 Litre SG 1.200£45.00 (ex VAT)
6117-1Sodium Nitrate Solution 1 Litre SG 1.27/1.28£14.00 (ex VAT)
6117-5Sodium Nitrate Solution 5 Litre SG 1.27/1.28£52.00 (ex VAT)
6108-1Zinc Sulphate Solution 1 Litre SG 1.200£15.00 (ex VAT)
6108-5Zinc Sulphate Solution 5 Litre SG 1.200£55.00 (ex VAT)
6118-1Zinc Sulphate Solution 1 Litre SG 1.27/1.28£17.00 (ex VAT)
6118-5Zinc Sulphate Solution 5 Litre SG 1.27/1.28£65.00 (ex VAT)
5636-10StatSpin - OvaTube x 10 £20.00 (ex VAT)
5636-50StatSpin - OvaTube x 50 £65.00 (ex VAT)
6604Small, plastic bowls x 10£1.80 (ex VAT)
052350ml plastic measuring cylinder£5.50 (ex VAT)