Horses and Worms-Strongyle Egg Shedding Rate(Part 2)

By Dr. John W. Byrd


After studying the samples that tested positive and negative in 2015, 2016 and 2017, Horsemen’s Laboratory’s staff decided to analyze the shedding rate of strongyle eggs during the same years.  The following charts and graphs are the results of that study.  There appears to be very little difference in the percentage of low shedders (negative up to 150/gm), medium shedders (200-500 eggs/gm), and high shedders (over 500 eggs/gm) on a month to month basis.  There may again be a trend for the months of March and September to have a slightly higher percent of high shedders.  This again may be due to the season of the year.


Since it has become evident that many of the worms that infect horses have developed resistance to many of the dewormers presently available new deworming protocols have been implemented that are based on fecal egg count results.  To establish what egg shedding category your horse fits in to Horsemen’s Laboratory recommends doing fecal egg counts on horses every 3 months until the egg shedding category for each horse is established.  This generally takes 3-4 fecal egg counts, then the deworming schedule for each horse can be determined as well as how often fecal egg counts need to be done to see that the horse remains in that category.


Once the shedding rate category is established for the horse Horsemen’s Laboratory recommends the following testing and deworming protocol.


Low shedders: Negative (no worm eggs found on counting chamber) -150 strongyle eggs/gm

Deworm once a year in late fall with a product that contains Ivermectin and Praziquantel to get bots and tapeworms that generally are notevident in a stool sample.  If the test indicates there are over 200 strongyle eggs/gm or any other worm eggs present, then retest 2-3 weeks after deworming.  Test again in late spring.


Medium shedders:  200 strongyle eggs/gm – 500 strongyle eggs/gm

Test 3 times a year and deworm after each test depending on results.


High shedders:  500 strongyle eggs/gm and above

Test 4 times a year before deworming and deworm according to results.


Remember no schedule fits all situations and other factors besides just eggs counts may come into play when one is developing a worm control program for horses.  For instance, this protocol is only for older horses (over 3 years) younger horses often need be considered high shedders.  Young horses (under 2 years) should be tested 4 times a year to keep tract of possible round worm infections and they often have higher strongyle egg counts.


In order to follow the new worm control program in horses, the first step is to start doing fecal egg counts on the horses periodically.  Horsemen’s Laboratory has been performing fecal egg counts through the mail for over 26 years.  Most of our clients have expressed a deep appreciation for how convenient our service is and the peace of mind that knowing their horses’ worm control program is effective.  If your horse has not been dewormed for 3 months or more now is the time to order our postage paid sample containers and have a fecal egg count done.  Order now at or call (800) 544-0599.


Strongyle shedding rate chart 3

Strongyle shedding rate chart 4