Worming, or more accurately, deworming is a confusing topic. The days of blanket worming should be over as it creates resistance to the products, and yet still this practice goes on, mostly out of confusion and mixed advice.

What are we trying to achieve?

The actual aim should be effective worm burden control. This isn’t a strive for a zero eggs per gram result every time we send of a poo sample; it’s about preventing worm related disease in our horses.

There is an increasing weight of evidence to suggest that there are potential benefits to exposure to a low parasite burden. There is little to no progress being made into the development of new drug classes and ever increasing levels of resistance to the drugs we already have access to; thus, if we continue managing our horses but answering the origin question “what do I worm with now?”, very soon we will run out of effective answers. Ever wished you didn’t have to worry about trying to muddled through the latest advice and worry about doing the wrong treatment at the wrong time – now you can whilst we do all the hard work for you!

To help all our clients achieve their goals without the headache, we’ve created a comprehensive worming programme. 

So what should we be doing?

Effective pasture management.

Removal of droppings from the pasture at least once a fortnight, will be effective in minimising pasture contamination with infective worm larvae. Droppings must be removed completely and only after storage for 6 months in an effective muck heap where the high temperatures will kill the eggs can the droppings be considered safe to spread on the pasture. Adequate grazing densities will promote the natural formation of grazed ‘lawns’ and un-grazed ‘roughs’ where most horses will choose to pass droppings.

Identifying and monitoring horses with significant parasite burdens.

Faecal worm egg counts: Faecal worm egg counts (WEC) form the basis of both identifying those horses with significant intestinal parasite burdens and monitoring them. WECs also play a role in monitoring the effectiveness of the anthelmintics and identifying resistance.

WEC results need to establish, more importantly than a specific numerical value those horses with significant intestinal parasite burdens as a separate population from those with no or acceptable levels of burden. What represents an acceptable burden may change throughout a horse’s life. WECs should be first performed in the spring (March – May). A fresh dropping sample should be collected in an airtight container or bag and kept cool and delivered the same day to your veterinary practice.

Horses with persistent low or zero WECs can have the interval between testing increased. Horses with high or significant WECs should be treated and re-tested in 2 – 3 months time; if they are high again, then interval worming should be used. Horses with very high burdens should be retested following worming to check for resistance to the wormer used, this is called a egg count reduction test.

Monitoring for Tapeworm: Traditional faecal WECs are not a reliable method for identifying tapeworm burden in the horse. However, an ELISA assay can be performed on blood or saliva samples for tapeworm antibodies which will identify horses with significant intestinal tapeworm burdens.

The modern approach to use of this assay is to test horses once in the spring. If this result reflects a low burden the horse is treated once yearly for tapeworm in the autumn. Those horses with a high result are treated twice yearly, once in Spring and once in Autumn. There is no requirement to repeatedly test these horses, but just base their on-going tapeworm treatment on the initial test results. Single dose praziquantel or double dose pyrantel are both effective in treating tapeworm.