Deworming With Fecal Egg Counts
Many peoples' idea of a parasite control program is to give their horse a dewormer and assume everything's taken care of. Many aspects of appropriate, logical and prudent anti-parasite programs are ignored with such an approach, which can lead to problems.
One often overlooked aspect of parasite control is regularly performing a simple, cost-effective and important test called a fecal egg count. This test involves identifying and counting different types of parasite eggs in a fecal sample by examining it microscopically. Results are reported in eggs per gram (EPG) of feces. In general, a low egg count (less than 200 EPG) indicates a low parasite burden, while a high egg count (500-1000 EPG, or greater) indicates a large number of parasites are present. High fecal egg counts suggest ineffective deworming (e.g. too long between deworming, inappropriate deworming drugs, underdosing of dewormers, failure to get the horse to swallow the dewormer), a lot of parasites in the environment or parasite resistance. Evaluation of fecal egg counts can give a general idea of the parasite burden in a particular horse or on a particular farm, indicate the effectiveness of the current parasite control program, and allow deworming recommendations to be tailored for a particular horse or farm. People recommend regular testing with deworming when egg counts are greater than 200 EPG, however, I don't think there is a consensus as to the best approach. Certainly, high EPG counts indicate a need for treatment or a change in the deworming program.
The fecal egg count reduction test (FECRT) is a way to assess parasite resistance to dewormers. Basically, it means performing a fecal egg count before and after (usually 7-14 days after) deworming. Egg counts should go down to close to zero after effective deworming. Failure to see this decrease indicates that the horse was not properly treated (e.g. it didn't actually swallow the dewormer or it wasn't given enough dewormer) or that some of the parasites may be resistant to the drug used. Early detection of resistance is very important so that the deworming program can be changed before health problems from uncontrolled parasites develop.
The main limitation of fecal egg counts is that some parasites, particularly tapeworms, do not produce many eggs, or they only produce eggs intermittently. Therefore, low EPG counts do not mean that there are no or few parasites of any type. That's why even deworming programs based on fecal egg count test results still use some "scheduled" deworming to eliminate these other parasites. Despite the limitations, fecal egg counts give excellent information for most of the parasites of concern, and can help a great deal with the design of effective, responsible deworming programs and evaluation of parasite resistance.
