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Deworming  – What’s new in parasite prevention?

The deworming strategy of  rotating dewormers and deworming your horse every 4-6 weeks is a thing of the past.  The parasite experts have determined that such a strategy has created resistance in a small population of strongyles.  As a result, we are killing off the weak worms and making the strong worms stronger.  Since 80% of the worms are carried by only 20% of the horses in a pasture, it is unwise to deworm every horse the same.
So, what’s the answer?  First, you must determine if your horse is  a “high” or “low” shedder by a fecal egg count.  Using a special slide with grids, we look at your horses feces  before the first deworming of the season and count the eggs.  Anything with an epg (egg per gram) of 200 or less is considered a low shedder.  Over 200 is a high shedder. A deworming protocol is then formulated based on your horse’s status. 

The steps for a good deworming protocol are as follows:
i) Prior to any spring deworming, bring in a sample of your horses feces from the last 24 hours for a fecal egg count (FEC).
ii) Based on the results, follow the schedule below on administering dewormer.
iii) Two weeks after deworming, submit another sample for another FEC (to make sure the dewormer is working).

April June October/ November
Pre-deworming Fecal? Yes Yes Yes
Dewormer Ivermectin None Moxidectin with Praziquantel
April June Aug Oct/Nov
Pre-de-worming fecal? Yes Yes Yes Yes
De-wormer Oxibendazole Pyrantel Ivermectin Moxidectin with Praziquantel

Oxibendazole Anthelcide
Fenbendazole Panacur
Ivermectin Eqvalan
Moxidectin Quest
Pyrantel Pamoate Strongid
Ivermectin + Praziquantel Eqvalan Gold
Moxidectin + Praziquantel Quest Plus

In 2011 in Simcoe County, there were two documented cases of horses infected with WNV.  Because it is a mosquito-born disease with serious consequences, we recommend including the WNV vaccine as part of your horse’s annual vaccination protocol.  If your horse has not received the vaccine in the last year, a booster is required 4 weeks after the initial vaccination.

Test your parasite knowledge:  True or False

1) “My horse should not have any worms”

It is normal for your horse to have some parasites.  To completely rid your horse of all parasites creates resistance to the dewormers.

2) Foals should be dewormed like adults

Foals are more intensely derwormed.  More information on foal deworming in next  month’s newsletter. Warning: NEVER use Quest or Quest Plus on foals under 6 months old

3) A horse’s mouth should be empty before giving dewormer.

Don’t let your horse spit out the dewormer by giving to a mouth full of hay


• Is your horse in foal? 
Vaccinations are very important – start your horse with EHV-1 vaccinations at month 5, 7, and 9 of gestation to protect against abortion, then vaccinate routinely 30 days prior to foaling

• Does my horse have Cushings disease? 
It may or may not.  Only a blood test can give an accurate answer.  More in next month’s newsletter.

• .Older horses have different nutritional requirements and may need a different grain (such as equine senior) as wells as soaked alfalfa cubes or beet pulp.  Remember – any diet change should be gradual to avoid potential gastric upsets

• Try to monitor your horse’s water intake to avoid potential impactions and colics.   A horse should drink about 2 water buckets per 24 hour period depending on weather conditions