McMaster Egg Counting Technique

Another 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 method is it is quick as the eggs are floated free of debris before counting, the disadvantage is you must use a special counting chamber.

1.     Weigh out 2 grams of feces.

2.     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.

3.     While mixing vigorously (you may want to put the solution into 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.

Counts done before and after anthelmintic treatment allow you to monitor for drug-resistance. Counts done between scheduled treatments allow you to monitor the worm load and thus allow you to change the treatment schedule if necessary.




4.     Wait 30 sec then count the total number of eggs under both of the etched areas on the slide. Focus first on the etched lines of the grid, then go down a tiny bit, the eggs will be floating just below the top of the chamber. Multiply the total number of eggs in the 2 chambers by 100, this is the eggs per gram (EPG).

5.     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 gms of feces and then multiplied by 100, the final result is eggs per gram of feces.

Click here for a video demonstration of the McMaster Egg Counting Technique


Commercial Sources of McMaster Slides:

1. Chalex Corporation 5004-228th Ave SE, Issaquah, WA. USA 98029,

2. Focal Point, Mr. Eddy Krecek, St. Kitts, West Indies email:

3. Prof. Antanas Vysniauskas, M.Marcinkevičiaus N0, 17-14, Vilnius LT-08412, Lithuania, Cell phone +370-618-24502, email:

4. FEC Source PO Box 2522, Hillsboro, OR 97123 USA. ( email: telephone: 1-503-407-1963

NOTE: Since McMaster slides are often difficult to find, these listings are being given as a service to those looking for a source for them. This should not be taken as an endorsement by the University of Pennsylvania.

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 photo above)


Copyright 2006 - University of Pennsylvania School of Veterinary Medicine, All rights reserved.
Faculty: Dr. Thomas Nolan
Students: Molly Church V'09, Diana Knight V'08, Douglas Gilson V'05, Chris Dykhouse V'04, Kimberly Mah V'00

Comments or Questions contact Dr. Tom Nolan at: