Fecal Examination Using the McMaster Egg Method

 

The McMaster Egg Counting Technique is a method for determining the number of nematode eggs per gram of feces in order to estimate the worm burden in an animal. The advantage of this technique is that it is quick as the eggs are floated free of debris before counting. The disadvantage is that you must use a special counting chamber.

  • Weigh out 2 grams of feces
  • Pass the feces through a sieve into a dish containing 60 ml of ZnSO4 or saturated salt solution. Lift the sieve and hold over the dish. Push out any remaining solution from the feces.
  • While stirring vigorously (you may want to put the solution in a flask to prevent spillage), take a sample of the mixture with a pipette and transfer it to one of the chambers of the McMaster slide. Repeat the procedure and fill the other chamber.
  • Wait 30 seconds then count the total number of eggs under both of the etched areas on the slide. Multiple the total number of eggs in the 2 chambers by 100, this is the eggs per gram (EPG).

    • The mathematics: The volume under the etched area of each chamber is 0.15 ml (the etched area is 1 cm X 1 cm and the chamber is 0.15 cm deep), so the volume examined is 0.3 ml. This is 1/200 of 60 ml. Since you started with 2 grams of feces and then multiplied by 100, the final result is "eggs per gram of feces".

    Above: McMaster slide

     

    Sources for McMaster slides are:   

    1. Chalex Corporation 5004-228th Ave SE, Issaquah, WA. USA 98029 http://www.vetslides.com/ ; 

    2. Mr. Eddy Krecek, Focal Point, St. Kitts, West Indies (http://www.mcmaster.co.za/) email: eddy@mcmaster.co.az eddy@mcmaster.co.az

    3.   Prof. Antanas Vysniauskas,  M.Marcinkevičiaus No 17-14, Vilnius LT-08412, Lithuania    Cell phone +370-618-24502   E-mail:   n.vysniauskas@gsm.lt

     Note:  The above listings are being given as a service to those looking for a source for this hard to find product, it should not be taken as an endorsement by the University of Pennsylvania.  The McMaster egg counting chambers may also be available through your local veterinary supply company.

If you want to have one of these slides made for you here are the particulars:

 They are usually made of Glass or Plexiglass:  2 pieces (2.5 cm by 7.5 cm) with 2 etched boxes (1 cm by 1 cm) on the under side of the top piece.  Some people make the bottom piece a little wider than the top piece to make it easier to load.  The etched boxes usually have 5 additional etched lines (subdividing the box into 6 sections) to make counting easier.  The etched lines should be as thin as possible so eggs are not hidden under them.   The 2 pieces are separated by  pieces (0.15 cm thick) placed at both edges and in the center between the etched boxes.     See the photo above.

 

 

© University of Pennsylvania  2004

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