PARASITE CONTROL IN HORSES  

Spring is a good time to re-evaluate your worm-control regime, here are some things to consider.  

BASIC PARASITE LIFE CYCLE 

Adult parasites live in the lumen of the gastrointestinal tract (gut), producing eggs. These eggs are passed in the faeces, where they hatch into larval stages and become infective on the pasture. These larvae live on the pasture, get eaten by a horse, and then become adult parasites again, which mature and produce eggs. 

Some of these worms have larval stages that migrate into the gut wall, into arteries or other organs. These are the larvae that will do damage to the horse. 

Testing your horses for parasites: Faecal Egg Counts (FEC) 

How 

With a faecal egg count, we determine the worm burden in your animal by counting the worm eggs per gram (EPG) of faeces produced. We prepare these samples and then examine them with a microscope, here in the lab. By counting the number of eggs present within the sample, we can determine the parasite burden/EPG.   

What 

We need a fresh fecal sample from your horse, that has been kept in the fridge between the time of collection and the time of testing.  

Why 

  • We can use the FEC results to decide which horses need drenching and which don’t.  

  • We can also use FEC to make sure the drench that you are using is effective and the worms are not resistant to it.  

When 

It is common practice to do a FEC every 8 - 12 weeks, to monitor the levels of parasites in your horses. A good rule of thumb is to plan to have a FEC done each season throughout the year.  

Parasite control 

The aim here is to keep the worm burden low. It is not possible to eliminate exposure to worms, as they are present within the environment, and it is okay for horses to be exposed to low numbers of non-resistant worms. 

Managing your pasture  
Proper pasture management provides a safe and effective way to keep the parasite burden to a minimum. Listed below are management practices that have been shown to lower the level of larval contamination on pastures: 

  • Picking up manure at least twice weekly, so the worm eggs are removed before they become infective. In the New Zealand climate, harrowing is not an effective way to get rid of parasites! 

  • Resting the paddock for 2-3 months 

  • Cross grazing. Ruminants can be used to ‘clean up’ horse pasture. Sheep and cattle can ingest equine worm larvae without getting infected, thereby decreasing pasture contamination. A good rotation schedule is to graze ruminants for a month after grazing horses. Then rest the paddock for 2-3 weeks before the horses go back on. 

  • Feed hay and hard feed off the ground to limit larvae exposure. 

Drenching 

The best way to know if your horse needs drenching, is through doing fecal egg counts. However, even with low EPG’s, your horses will need drenching once a year, as not all worms show up on FEC.  

There are multiple different types of drench available, that work on different types of worms. Which wormer is best to use can be dependent on lots of variables, like the time of year, age of your horses, number of horses on your property, FEC results and other factors.  

Your vet can give you tailored advise on which drench is the best option for you and your equines!