LABOKLIN Service ID: 2632

The modified McMaster method is used for

  • egg count (e.g. to carry out selective deworming)
  • egg count reduction test (egg count before and after deworming) to test effectiveness of anthelmintic treatment




count of worm eggs by counting chamber after enrichment by flotation


1 day


  • Egg count: This method is primarily used in horses, sheep and other farm animals to carry out targeted or selective deworming to reduce the development of resistance to strongyles. In targeted or selective deworming, individual deworming is only carried out if there are > 200 eggs per gram of faeces.
    If all animals of a population that have a worm infestation are dewormed, only resistant worms survive. However, if only animals that have a more severe worm infestation are dewormed, an untreated worm population is also found in the animal population, which reduces the selective advantage of resistant worms and thus counteracts the further increase in resistance.
  • Egg count reduction test: 10 – 14 days after treatment, further individual samples (selective deworming, see above) are tested using the modified McMaster method. If high egg counts are still present, anthelmintic resistance should be considered. This method is mainly used in the large animal practice in ruminants, horses and pigs.
    Even if deworming does not take place selectively at the level of the individual animal but, for example, of groups of animals, regular monitoring of the effectiveness of anthelmintics by means of an egg count reduction test is recommended.