• The McMaster Method is the most widely used method for nematode fecal egg counting (FEC) or coccidia faecal oocyst counting (FOC).
• The method uses a specific counting chamber (McMaster slide) to examine microscopically a known volume of a fecal suspension for helminth (worm) eggs and coccidia oocysts.
• If a known weight of feces and a known volume of flotation fluid are used to prepare the suspension, then the number of worm eggs per gram (epg) or coccidia oocysts per gram (opg) of the feces can be calculated by multiplying the number of eggs/oocysts under the marked areas in the slide chamber by simple conversion factors.

Uses

• The demonstration and counting (quantitative) of helminth eggs or coccidia oocysts in fecal samples.
  • Trichostrongyle nematodes (Ostertagia Ostertagia ostergagi, Cooperia Cooperia spp, Haemonchus Haemonchus placei, Trichostrongylus Trichostrongylus axei, Nematodirus Nematodirus spp).
  • Strongyle nematodes (Chabertia, Oesophagostomum Oesophagostomum, Bunostomum Bonostomum).
  • Other gastrointestinal nematodes (Toxocara, Strongyloides Strongyloides spp, Trichuris Trichuris spp).
  • Tapeworms (Moniezia).
  • Fluke (Fasciola) Fasciola gigantica Fasciola hepatica.
  • Coccidia oocysts (Eimeria) Eimeria bovis Eimeria zuernii.
• Used as part of parasite control programmes.
• Used in investigation of calves with weight loss/diarrhea.
• Used to identify potential wormer resistance and suspect loss of efficacy (SLOE) to anthelmintics by means of fecal egg count reduction (FECR) test.

Advantages

• Allows the number of parasite eggs/oocysts per gram of feces to be calculated.
• Generic identification is possible with some parasite species.
• FECs or FOCs allow identification of cattle with high parasite infections and guide targeted treatments.
• Cattle with low or zero parasite counts can be identified avoiding unnecessary antiparasitic treatments, but beware of limitations of the techniques and the risk of disease caused by immature/larval stages.

Disadvantages

• Only patent infections are identified. 
• For nematode fecal egg counts:
  • Numbers of eggs reflect only the presence of adult female worms in the intestinal lumen despite potentially large numbers of immature worms/larvae being present and;
  • Do not always indicate the number of worms present in the animal from which the feces came, i.e. there is no direct linear correlation between actual worm burden and the FEC. However, cattle with FEC <200 epg have significantly lower intestinal worm burdens that cattle with FEC >500 epg.
• Numbers of trematode or cestode eggs, and protozoa cysts in feces, may provide less reliable estimates of parasite burdens due to intermittent excretion.
• Not all eggs/cysts from the various different parasite species are the same weight.  Heavier eggs, and some protozoa cysts, will not float as well in lower specific gravity solutions. This will decrease their counts.
• Worm egg or protozoa cyst counts will also be influenced by the volume of feces passed each day, intestinal ingesta passage rate, and the way the eggs/cysts are distributed through the feces.
• Trichostrongyle and strongyle eggs cannot be differentiated to genus or species level unless subjected to fecal culture and larval identification.
• Coccidia oocyst counts, on their own, are insufficient and oocysts should be identified to species  .

Technical problems

• Fecal samples should be fresh and preferably either collected from the rectum or from freshly voided samples.
• Ideally representative numbers of samples should be collected from a group of animals with a minimum of 10 samples of approximately 10 g each.
• Each sample must be clearly identified.
• Samples can be kept in the refrigerator at 4^oC for up to 5 days without change in numbers and morphology of the eggs/cysts.

Alternative techniques

• Fecal smears can be used to demonstrate the presence of helminths and protozoa and help identify some species/groups that are present. Although it is quick and simple it is a relatively insensitive technique.
• Simple test tube flotation techniques are semi-qualitative tests for detecting both helminth eggs and protozoa cysts. Includes several commercial test kits (Ovassay^TM, Ovatube^TM).
• Other quantitative fecal egg counting techniques and modifications are reported with additional commercial kits available e.g. FecPak^TM, Flotac^TM, Parasep^TM, Paracount^TM).
• The Baermann technique Baermann technique allows the separation of larvae from fecal samples. It is used in the diagnosis of lungworm infection Lungworm and for fecal culture and larval identification.
• The sedimentation technique is a qualitative and quantitative method for detecting trematode eggs in fecal samples.

Time required

Preparation

• 10-15 min.

Procedure

• 10-15 min.

Decision taking

Criteria for choosing test

• Assessment of adult worm burden or coccidia infection Feces: parasitology in individual animals or group of cattle and monitoring of pasture contamination.
• Assess success of preventive programs, including anthelmintic administration as part of FECR test.
• Quarantine measures for new arrivals to determine egg or oocyst shedding.
• Investigation of calves with weight loss, altered fecal consistency.

Risk assessment

• Fecal samples can contain hazardous material and therefore appropriate health and safety measures should be taken.