Montesano & Tallarico, D.V.M., LLP

305 Old Willets Path
Smithtown, NY 11787



Deworming Recommendations:


1. Non-Chemical Parasite Management:

  • Rotate pastures

  • Cross graze pastures with ruminants if possible

  • Remove manure frequently 

  • Harrow/drag pastures in hot/dry weather and keep horses our for 2 months 

  • Avoid overstocking pastures

2. Measure the success of parasite control by doing fecal analysis at least once a year. 

Fecal egg count--an estimate of the number of parasite eggs shed by the horse 

  • Talk to your veterinarian before doing a fecal analysis to be sure enough time has passed since your horse's last deworming for eggs to have reappeared in the feces. This Egg Reappearance Period differs depending on the dewormer used.Cyathostomin egg reappearance periods (ERP) for equine anthelmintics: 








Usual ERP when drug is effective


4-5 weeks

4-5 weeks

6-8 weeks

10-12 weeks

ERP when drug was first introduced


6 weeks

5-6 weeks

9-13 weeks

16-22 weeks

3. Treat for tapeworms once a year with use of a dewormer containing praziquantel (Zimectrin Gold or Quest Plus).

4.  Treat the horse with a dewormer that acts against bots.

A well-planned deworming program is your best defense against bots. There are several brands of dewormer that control bots, but there are only two active agents with label efficacy against bots: ivermectin and moxidectin. Both agents paralyze the immature forms of the flies wherever they may be, either in the mouth or the gastrointestinal tract. Unable to move, they cannot eat and soon die.
To be effective, the timing of the treatment needs to correspond to the times when the larvae are most likely to be present within the horse. The usual advice is to wait until after the first killing frost because that will eliminate one source of infection--the egg-laying adult flies. We recommend treatment in mid December, January. By that time most regions will have experienced a frost.


5. In their encysted larval stage, small strongyles (cyathostomes) are only susceptible to a couple of dewormer categories. Given drug resistance findings world-wide, moxidectin (Quest) would be drug of choice in most cases. Treatment for the encysted larvae are recommended in the fall near or at the end of the grazing season, before going into the winter. 

6. Don't use the same pasture or paddocks year after year for mares and foals. This allows build-up of a high level of ascarid eggs, which can survive between years and infect new foals being born in the Spring. 

**Note: The two parasites of most concern in adult horses are the small strongyles (encysted strongyles, cyathostomes) and tapeworms. In young horses the parasite of biggest concern is the ascarid. The best way to determine the deworming schedule for your horse is to involve your veterinarian and to perform fecal egg counts (FEC) to determine: 1.) Dewormer efficacy in your equine operation, 2.) monitor for presence of ascarids in young horses, and 3.) identify low, medium or high strongyle egg shedders among adult horses. A surveillance-based deworming program allows the use of less dewormer, can save money, and ensures that the program is effective.