Bovis ISSN 2398-2993

McMaster worm egg count

Synonym(s): Fecal egg count, FEC, FWEC

Contributor(s): Mike Taylor , Andrew Forbes


  • 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.



  • 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.


  • 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  .


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Further Reading


Refereed Papers

  • Recent references from PubMed and VetMedResource.
  • Dunn A & Keymer A (1986) Factors affecting the reliability of the McMaster technique. J Helminthol 60, 260-262.
  • Pereckiene A, Kaziunaite V, Petkevicius S, Malakauskas A, Sarkunas M & Taylor M A (2007) A comparison of modifications of the McMaster method for the enumeration of Ascaris suum in pig faecal samples. Vet Parasitol 149, 111-116.

Other sources of information

  • Taylor M A, Coop R L & Wall R L (2016) Laboratory Diagnosis of Parasitism. In: Veterinary Parasitology. 4th edn. Wiley-Blackwell, UK. pp 259-262.
  • Gibbons L M, Jacobs D E & Fox M T & Hansen J (2015) McMaster Egg Counting Technique. In: The RVC/FAO Guide to Veterinary Diagnostic Parasitology. The Royal Veterinary College, UK. Website:
  • Ministry of Agriculture, Fisheries and Food (1986) Reference Book 418: Manual of Veterinary Parasitological Laboratory Techniques. 3rd edn. HMSO, UK. pp 12-15.
  • Thienpont D, Rochette F & Vanparijs O F J (1986) Diagnosing Helminthiasis by Coprological Examination. 2nd edn. Janssen Research Foundation, Belgium. pp 205.
  • Whitlock H V (1948) Some modifications of the McMaster helminth egg-counting technique and apparatus. J Council Sci Indust Res Australia 21, 177-180.
  • Gordon H M & Whitlock H V (1939) A new technique for counting nematode eggs in sheep faeces. J Council Sci Indust Res Australia 12, 50-52.