PARASITE CONTROL PROGRAM

For several decades, equine deworming programs have focused on rotational deworming strategies in which horses are dewormed with different anthelmintic classes at strategic intervals.  This approach is no longer sustainable because we now know that rotation does not slow, and in fact, actually selects for resistance to all drugs in the rotation.  Slow rotation, in which a single anthelmintic is used for an entire year, is also concerning due to the prevalence of small strongyle resistance. 

There are no new deworming products in the pipeline, so we cannot just wait and hope the next generation of dewormers will solve the resistance problem. 

In order to combat resistance before it becomes so widespread that we have no effective dewormers, it is time to adopt a new approach.  We will identify and treat those horses that are the heavy shedders of parasites on a frequent basis and reduce the treatment frequency for the average horse that boasts reasonable immunity to parasites to twice a year.  This will be monitored by repeat fecal examinations. 

Program Implementation:

We need to identify which horses belong to which category.  This will be done by performing fecal examinations on every horse several times from April through December.  These fecal examinations allow us to perform a Fecal Egg Count (FEC), which tells us how many parasite eggs per gram (EPG) of feces each horse is harboring.  Low shedders (those with some degree of natural immunity) are those horses with less than 200 EPG.  These horses should have fecals done in April, July, September, and November.  High shedders have more than 200 EPG, and will be monitored more often on a case by case basis.

After the first fecal is run in April, low shedders will be given a dose of moxidectin with praziquantel (Quest Plus).  They will then have follow up fecal examinations in July, September, and November.  As long as the egg count stays below 200, they will be dewormed again in November with ivermectin/praziquantel (Equimax, Zimectrin Gold).  If at any point the egg count starts rising, we will make additional recommendations.

High shedders will be given a dose of moxidectin/praziquantel.   They will continue to have fecal exams done routinely and will be dewormed more frequently according to their fecal egg counts.  If they have particularly high FEC’s, we will run more frequent fecals and adjust the deworming program until we are sure the FEC has dropped low enough. 

Foals will also be treated less often than in the past.  After they reach the age of one year, they will be dewormed as an adult, but should not receive moxidectin/praziquantel until they are 18 months old.

Moxidectin should not be used in miniature horses, miniature donkeys, horses less than 18 months of age, or pregnant mares.  We will substitute ivermectin for these individuals.

Summarizing Tables:

Adult Low Shedder

Adult High Shedder

Foal

New Arrivals on the Farm:

1.     Permanent additions: Submit fecal and deworm with Moxidectin/Praziquantel.  Repeat fecal exam in 10-14 days before turning horse out with herd.

2.    Visiting horse: Can be transiently prevented from contaminating pasture with ivermectin treatment which will last up to 6-8 weeks.  Must wait 10-14 days before turning horse out with herd.

Daily Dewormer:

            If your horse is on a daily dewormer the same fecal schedule as above should be followed and the adult low shedder schedule for paste deworming will be followed unless elevated egg counts are detected.

It is important to remember the importance of providing a clean environment. 

This is one of the most important antiparasitic tactics.  Do your best to keep your paddocks and pastures free of manure.  Do not spread manure unless it can be done in a part of the field that won’t have exposure to horses for a month.  Only drag pastures during dry weather.

This schedule will probably undergo modifications as more research and more resistance data are published.

We can provide you with plastic cups for fecal sample submission.  Please write horse’s name on the cup with a black magic marker.