Module 3: The Quantitative Fecal Exam

Module 3.3: Modified McMaster’s Technique

Modified McMaster’s technique

In today’s laboratory we will be performing the Modified McMaster’s technique (see pg. 12 or video below) to quantify the number of epg in the feces provided. Once you have prepared your fecal mixture and allowed the mixture to float using a McMaster’s slide for 30 minutes you will begin counting the number of eggs found in each chamber.

Please watch the following video before the laboratory to gain an understanding of how you will perform the procedure. We will not be reviewing this technique in class.

This video describes the technique we use to count the eggs using a McMaster’s slide. Please forward to 3 minutes 34 secs. We will not be reviewing this technique in class. 

Below is an image of a McMaster’s slide. Each chamber holds 0.15 mL of fecal material. Additionally, each chamber has 6 vertical lanes per grid. Thus, each grid is calculated so that you can enumerate the number of eggs or oocysts per 0.15 mL of fecal material.

 

McMaster’s slide with two chambers. Each chamber has 6 vertical lanes
McMaster’s slide

You will count the number of eggs or ova seen in each chamber (the total of the 6 vertical grids). Eggs or ova that touch the grid lines or are found outside of the counting chamber are excluded from the total number. The total number of each type of ova is tallied for the calculation to the following formula.

Eggs Per Gram (EPG) Equation

\frac{\left(Eggs_{chamber\:1}+Eggs_{chamber\:2}\right)}{0.3 \:mL}\times\frac{total\:volume\:(mL)}{feces\:weight\:(g)}=epg

Let’s look at an example:

Fecal mass: 2 grams

The total volume of fecal solution: 60 mL

Count

Chamber 1

Chamber 2

Total (Chamber 1+2)

EPG
Strongyle-type
 5 2 7 700
Coccidia
 30 40 70 7000
Others (List)
Nematodirus
 1 0 1

 

Case Example Calculations

Strongyle-type:

\frac{(5+2)}{0.3\: mL}\times\frac{60\:mL}{2\:g}=700\:epg

Coccidia:

\frac{(30+40)}{0.3\: mL}\times\frac{60\:mL}{2\:g}=7000\:epg

 

Knowledge check

Key Takeaways

  • The McMaster’s and Wisconsin techniques are special types of fecal flotations that allow fecal egg quantification
  • The McMaster’s is a dilutional technique that is commonly used when a high egg burden is suspected
  • The results from the two techniques are not interchangeable (e.g. you cannot compare results)
  • These tests are validated for coccidia and Strongyle-type eggs
  • These tests should be interpreted over several time points at the herd level to guide antiparasitic recommendations
You have now reached the end of Module 3. If you are enrolled in CVM 6925, please go to the Canvas page and take the quiz: “Module 3: Quantitative fecal quiz.” There is an assignment that accompanies the in-person laboratory for this module.

 

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Clinical Veterinary Diagnostic Laboratory Copyright © 2021 by Erin Burton and Anna Lalande is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License, except where otherwise noted.

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