November Newsletter

The McMaster's Fecal Egg Count Technique

by Catherine Hall DVM

Fall is in the air!  And with fall brings cooler weather, trail riding, fall shows and routine maintenance needed for your horses.  Don’t forget about vaccines, coggins tests, dentals and fecal egg counts for your horses.

Here at CGES, we recommend an every 6 month vaccine protocol for most of our routine vaccines.  The encephalitis’ (Eastern and Western equine encephalitis), tetanus, and West Nile virus are the core of any good vaccine protocol here in middle GA.  If you travel a lot, board your horse where there is a lot of horses in and out, or heavily show, we recommend influenza and equine herpes virus (rhinopneumonitis) also.  Rabies vaccination is also highly recommended in horses, but it is only a once a year vaccine.  So, if you’re unsure about what time of the year your horse receives their rabies vaccine, just give us a call.

As for fecal egg counts…a lot has changed over the years on deworming recommendations.  Once there were very few dewormers available to use on horses.  This made things easy.  Then in the early 80’s, ivermectin was introduced onto the market.  This was the new anthelmentic which would eradicate all parasite problems, in theory.  And moxidectin was introduced in the early 90’s.  As these new anthelmintics were introduced, the idea of rotational deworming developed as a thought that this was the better way to get all parasites.  However, this idea only increased our ability to produce resistant parasites!  And with this resistance arises the problem that there are no new anthelmintics on the back burners like in times past.

Strategic deworming is newest theory and method to help control the resistance we have already began to create.  Studies show that only 20% of the horse population harbor 80% of the parasite population.  This statistic is what strategic deworming has been developed around.  Treating the horses with high to moderate FEC depending on the time of year, and then the rest of the population will regulate themselves.

We recommend two FEC per year…one in the fall and the other in the spring.  The fall FEC is the most important, as the temperatures are falling, allowing for the Strongyle eggs which hatch to be picked back up by the grazing horses.  Depending on a horses FEC in the fall, depends on how we deworm.  If they are high shedders, they will likely be dewormed at the time of the count and then in early winter after the first frost to eliminate any tapeworms which may have been picked up during the summer and fall.

This should take care of all parasites through the winter.  Then in spring, another FEC is recommended.  Only those who are considered high shedders are dewormed at this time.  All others should be fine due to the fact that as the temperatures begin to rise, the larvae the eggs hatch cannot survive.  Therefore grazing horses are not picking parasites back up through the late spring and summer months.

However, always keep in mind that there may be additional recommendations and additional FEC performed on some horses.  Depending on the egg count and anthelmentic used, we may recommend repeating the FEC sooner during the first year of getting horses on this program.  If we feel there is a resistance scenario going on, we may need to check the efficacy of the anthelmintics being used.  

So, go out, collect your fecal samples (only 1-2 fecal balls needed), and bring them into us today.  Or if we are out your way, we’d be happy to collect the samples for you.

Now, let’s travel through the process with Rachel Oliver, our veterinary technician.  The type of test performed is called a McMaster’s fecal egg count.  Each test is done for an individual horse, therefore you cannot combine samples.  One fecal ball is needed per horse in a nicely labeled bag.  

First, Rachel measures out 26 ml of a special sodium nitrate solution which will cause the eggs be suspended but not burst.






Next, 4 grams of fecal material is added to the solution.






Things are mixed well and the mixture is drawn into a one milliliter syringe for administration into a special slide.





This slide, called the McMaster’s slide, has grid lines which help
 to better quantify the sample.  The slides have 2 chambers, with 1 cm2 gridlines.  0.5 ml of the mixture is placed on each half of the slide giving a 0.15 ml sample per each grid line.




The grid lines are read with the microscope looking for parasite eggs.  The number of eggs are counted and with some simple math, it is determined how many eggs per gram a sample of feces contains.  This test is only specific to a number as low as 25 eggs per gram.   




We have additional information available at the clinic about this process and strategic deworming.  Please feel free to drop in and pick them up!