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The McMaster Egg Counting Technique
Trinity recommends The McMaster Egg Counting Technique which is a method for determining the number of nematode eggs per gram of faeces in order to estimate the worm burden in an animal. The advantage of this technique is that it is relatively simple as the eggs are floated free of debris before counting. The disadvantage is that you must use a special counting slide. The McMaster slide has two chambers, each with a grid etched onto the upper surface.
Firstly 2 grams of faeces are weighed out. The faeces are then put through a sieve into a dish containing 60 ml of ZnSO4 or saturated salt solution. The sieve is held over the dish and any remaining solution is removed from the faeces.
While stirring vigorously a sample of the mixture is taken with a pipette and transfer to one of the chambers of the McMaster slide. The procedure is repeated and the other chamber is filled. After 30 seconds the total number of eggs under both of the etched areas on the slide are counted using a microscope. The total number of eggs in the 2 chambers are multiplied by 100, this gives the eggs per gram of faeces.
Mathematically 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.
Amounts and concentrations of fluid and faeces can be changed to suit individual laboratories and circumstances. This requires a change in the mathematics.