McMaster Technique
Aims: The modified McMaster technique is used for the quantitative assessment of the parasitic eggs and oocysts present in the faeces of farm animals and horses for the calculation of Fecal Egg Counts (FECs) to determine an animal’s egg shedding burden.
Materials:
- Faecal sample
- McMaster slide
- Saturated solution of NaCl (m.p. 1200)
- 2 cups
- 1 wooden tongue depressor
- 1 fine mesh strainer (250 µm)
- 1 Pasteur/transfer pipette
- Tally click counter
Procedure:
In one of the two cups, thoroughly mix (homogenize) the faeces with a wooden tongue depressor into a saturated solution of NaCl (S.G. 1200) using a ratio of 1:15 of faeces:solution (e.g., 3 g of faeces in 42 mL of solution). Pass the mixture through the solution with a strainer, 4-6 times, each time transferring the contents from one cup to the other. Keep the suspension thoroughly mixed and collect 1 mL of the liquid using a Pasteur/transfer pipette. Fill each well of the McMaster slide*, ensuring the chamber is entirely filled and there are no air bubbles present. Once each chamber is filled, allow the slide to stand for 5 minutes before counting, so the parasitic eggs within the solution can float to top of the chamber.
*McMaster slides are composed two superimposed slides that contain precisely measured reading chambers with grid lattices present to assist in egg counting. The slide consists of two chambers, each with a holding capacity of 0.5 mL.
Results:
Examine the slide at 10x objective and count all the target parasitic eggs/oocysts present using the tally click counter. When examining the grids, only count eggs that fall within or overlaying the grid lines within each chamber.
The dilution factor between the amount of faecal material and floatation solution used will guide the calculation equation to determine eggs per gram of faeces (EPG). To determine the EPG, multiply the total number of targeted parasitic eggs/oocysts counted by the multiplication factor divided by the grams of faeces used.
To determine the EPG:
- Number of eggs x 50  if both grids were examined
- of eggs x 100  if one grid was examined
- of eggs x 15  if both chambers were examined in their entirety
- of eggs x 30  if only one chamber was examined in its entirety
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*The greater the reading surface, the higher the sensitivity of the technique.
*Do not use a higher power than the 10x objective, as this may crack the slide.
References:
Mc Master Technique:
Euzeby, 1981. Diagnostic expérimentale des helmintoses animales. Travaux pratiques d’helmintologie vétérinaire. Livre 1. Paris, France.
MAFF, 1986. Manual of veterinary parasitological techniques. Technical Bulletin No.18. Third ed. Her Majesty's Stationery Office London, UK
Vadlejch, J., Petrtyl, M., Zaichenko, I., et al. (2011). Which McMaster egg counting technique is the most reliable?. Parasitology Research. 109: 1387-1394.