The Scoop On Fecal Egg Counts


I have read a lot on Fecal Egg Counts over the past few months.  Could you discuss the appropriate use of counts here in Colorado?



In the last Ask a Vet, we discussed rotational deworming and its application here in Colorado.  Fecal Egg Counts (FEC’s) are a tool that we use to help us direct rotational deworming.  A FEC is a test the counts the actual number of parasite eggs within the horses’ manure.  This is done by submitting a small sample of manure to your veterinarian.  Your veterinarian then runs a floatation test on the sample and counts the number of parasite eggs that are present in that sample, reported as eggs per gram of feces.  The ideal time to run the test is about 3 months after the last dose of dewormer was given, which allows an appropriate timeframe for parasite eggs to reappear.  This gives you the baseline amount of parasites that your horse has present without interference from any deworming drugs.


At this point, each horse within a herd can be ranked in regards to the amount of parasite eggs that they are shedding.  This ranking is dependent upon each horse’s individual natural immunity to internal parasites.  The extended timeframe since the last deworming gives us insight into the immune system of the horse and its ability to naturally fight off parasites, rather than the efficacy of the last dewormer used. 


We will generalize and place each horse into a broad category of parasite shedding.  If, a horse is found to be a “low” shedder, then it is possible that the horse can be dewormed less frequently (once every 6 months).  These horses have a higher natural immunity to parasites, and are less likely to accumulate a large number of parasites within their system.  Many horses fall in the “moderate” shedder category.  Normal deworming for these horses would be considered quarterly rotational deworming (previously discussed here), where the horse is dewormed about every 3 months.  The “high” shedders are the problem horses.  These are often older or immune compromised horses, which are unable to fight of parasites.  These horses should be dewormed more frequently (up to 5 or 6 times a year). 


The second part of the Fecal Egg Count is the egg reduction test.  After the “baseline” is established, a second test sample is taken 10 to 14 days after deworming.  This sample allows us to determine if there is a drug resistance problem within your herd.  If the dewormer that you gave is effective, then a horse should have a significant (>90%) reduction in the number of eggs seen within the manure.  If there is less than 90% reduction in the number of eggs, then the dewormer that you used lacks efficacy or you have resistant parasites to that dewormer present in your horse.  In combination with appropriate rotational deworming, Fecal Egg Counts can help guide parasite control for your horse, and potentially save you some money on deworming products.  More importantly, FEC testing can help you to more closely monitor you horses’ health, and potentially help save you money in the long run.

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