Due to the increase in anthelmentic resistance in equine helminths the World Association for the Advancement of Veterinary Parasitology (WAAVP) guidelines recommend the use of Fecal Egg Count Reduction Testing. This involves doing a fecal egg count before and after treatment with an anthelmintic. The initial egg count determines the parasite load.  Any of the quantitative methods would be appropriate in doing a FECR test (McMaster, Wisconsin or Modified Wisconsin).  Be sure to use the same technique for the first count and all subsequent counts. Horses are classified as low contaminators (fecal egg count (FEC) of <200 eggs per gram (EPG) of faeces), moderate contaminators (FEC of 200-500 EPG faeces) or high contaminators (FEC >500 EPG faeces). It is not usually recommended to treat horses with FEC less than 250 EPG of faeces. Horses with FEC greater than 250 EPG of faeces are then treated with an appropriate anthelmintic. Typically 10-14 days post-treatment another fecal egg count is performed. If the anthelmintic used is efficacious then there should be a reduction of 90-95% in the fecal egg count between the pre and post-treatment tests. If the egg count has not been reduced by that degree then there is some degree of resistance in some of the parasites and the use of that anthelmintic should be discontinued.

 

This technique can be used for other hosts as well, as a measure of drug resistance or a measure of client compliance.

von Samson-Himmelstjerna, Georg. 2012 Anthelmintic resistance in equine parasites – detection, potential
clinical relevance and implications for control. Veterinary Parasitology 185: 2-8

Vidyashankar A.N. et al (2012). Statistical and biological considerations in evaluating drug efficacy in equine strongyle parasites using fecal egg count data. Veterinary Parasitology 185: 45-56.