Parasite Control

DEWORMING / FECAL EGG COUNTS AND PARASITE CONTROL

Deworming Newsletter January 2015- click this link to see

 What is targeted deworming?

Targeted deworming is a deworming plan to only treat the horses that have the most parasites.  In this plan, each horse is treated as an individual as opposed to blanket deworming of all horses on a property. 

Why should I switch to targeted deworming?

The interval (or rotational) deworming programs were developed in the 1970’s to control large strongyles (Strongylus vulgaris).  These programs were incredibly successful, and large strongyles are no longer considered a major problem in horses.  As effective as rotational deworming was against large strongyles, it is not effective against small strongyles (cyathastomes), tapeworms, bots, and pinworms.  Deworming on a rotational basis has lead to a high level of anthelminthic resistance.  This is not just an equine problem, but also highly prevalent among small ruminants.  Due to the large amount of resistance, it has become prudent to become more judicious with the use of our existing dewormers to maintain their effectiveness. 

What is the rationale behind targeted deworming?

Each horse has a unique immune susceptibility to parasites, regardless of the frequency of deworming.  It is estimated that 20% of horses are responsible for 80% of parasite contamination.  Up to 50% of horses may shed few to no parasites.  Research has also shown that a small number of parasites may increase a horse’s immunity to a large worm burden.  Maintaining a low level fecal egg count may also cultivate a parasite population that can become less resistant to dewormers.

Environmental Parasite Control

• Pick manure out of pastures regularly (at least weekly)
• Rotate pastures (leave pastures vacant for 4 weeks after)
• Do not overstock pastures (recommended 1-3 acres/horse)
• Isolate new horses and perform fecal egg counts before putting out with a herd.  Isolating horses for 2-3 weeks prior to introducing a new horse also screens for other contagious diseases
• Compost manure before spreading (heat kills parasites)
• Do not drag occupied fields.  Only drag fields during hot, dry summer days.  Dragged pastures should be vacated for 4 weeks.

Fecal Egg Counts

Fecal egg counts should be done at least 12 weeks from the last deworming (for moxidectin).  Fenbendazole and pyrantel can be rechecked in 4 weeks, ivermectin in 6-8 weeks.

Low Shedders <200 EPG
Medium Shedders 200-500 EPG
High Shedders >500 EPG

Horses tend to follow the same pattern due to innate susceptibility.  So the low shedding horse will tend to be a low shedder every year, and the high shedder will always tend to be a high shedder.  So because of this, after the first year of testing and deworming, you will know who on the farm will be a low, medium, and high shedder.  The low shedders will only need a FEC once a year or once every other year after the first year.

How do I test for resistance on my farm?

1. FEC all horses on the farm.  You will then identify your medium and high shedders, which will be the participants in the testing
2. Deworm (start with the most commonly used dewormer on the farm).  To properly test for resistance, you will have to go through all the dewormers.
3. Recheck FEC after 2 weeks.  There should be a >90% decrease in eggs on the fecal.  If there is a <80% decrease in eggs, the parasites on the farm are resistant to that dewormer, and that dewormer should not be used, or only be used in combination with another dewormer in the future.