To Worm or Not to Worm?

Mar 7, 2019 | Horse Care

Historically most horse owners have wormed their horses every few months, (so called
‘interval dosing’), without checking the worm burden of the horse first.
However evidence is increasing all the time that we should change our policy, and Stockley
has discussed this with Arundel Equine Hospital:

  1. Worms are becoming ever more resistant to all the groups of wormers primarily due to
    the overuse of wormers. There are no new wormers on the horizon, so we need to use
    existing wormers as efficiently as possible to minimize the development of resistance.
  2. Horses do not need to have a zero worm burden. A low worm burden helps stimulate immunity and is probably beneficial. A faecal worm egg count (FWEC) of 100-200 eggs per gram (epg) is considered acceptable by most clinicians.

In several recent surveys 85-90% of faecal samples had an egg count below this threshold
and therefore worming was unnecessary. We are therefore working with the support of our
local Vets to change from Interval dosing to Targeted Dosing.


Targeted Dosing

A better way of worming is to do regular Faecal Worm Egg Counts (FWECs) and only worm horses with a significant worm burden (‘targeted dosing’). Even allowing for the extra costs of egg counts this works out cheaper for most horses as it reduces the use of wormers. It also slows the development of resistance and is better for the horse population as a whole. Our findings agree with recent surveys that showed that 80% of worms are carried by only 20% of horses i.e. in a group of horses all kept under the same conditions only one may have a high worm burden. FWECs can identify these horses which need to be tested more regularly. They have a lower immunity to parasites and will probably need to be wormed more frequently than other in-contact horses.


How do you implement a targeted dosing programme for your horse?

Programmes vary slightly depending on individual circumstances. Initially FWECs should be performed at 3 month intervals. In small yards with good pasture management and a low worm burden the interval can increase to every 6 months. Larger yards may need to continue on more frequent testing.

Stockley Outdoor & Equestrian can provide their customers with a small FWEC kit with  everything that you need. All you need to do is place fresh faecal samples (only 5 grams, not a whole rose bed full!) into the small sample pot provided and then post it in the Freepost jiffy bag to our partner Westgate Laboratory. The sample(s) will be tested in the lab the same day they arrive and results will be sent back to you with advice and prescription by email immediately by our Animal Medicines Advisor (AMTRA trained Specially Qualified Person).


What are the limitations of FWEC?

Faecal worm egg counts are for strongyles (redworms) and ascarids (roundworms) The redworm is a serious threat to your horse whilst the roundworm can be a significant problem for youngsters with naïve immune systems. Egg counts do not detect immature, encysted worm larvae which are not producing eggs. If the horse’s worm history is unknown, especially young horses which are more susceptible to encystment, initial worming is recommended.


How about other worms?

Our partners at Westgate laboratories can also test for Lungworm and liver fluke or Pinworm, just ask in store for details and our staff will provide the correct pack for your needs. If the horse does not get wormed because it has a low egg count you will not remove bot larvae that live in the horse’s stomach over the winter. Bots may not be pathogenic but most owners prefer to remove them.


And Tapeworms?

FWECs do not quantify a horse’s tapeworm burden although segments appear intermittentlybin faeces. In the past it was only possible to assess the tapeworm burden using a blood test so in practical terms it was easier to interval dose with a tape wormer in the Autumn after the first frost or possibly twice per year. An untreated tapeworm burden can cause colic.


New Tapeworm Saliva Test

Now at Stockley we have teamed up with EquiSal Laboratories to provide a Tapeworm Test
Kit based on saliva. It works in just the same way as the FWEC using Freepost envelopes
and again the results together with advice and any prescription are available the same day
that the sample arrives at the lab.


So what year round worming policy do we recommend?

  1. All new horses and horses with an unknown worming history should receive a
    combined round/tape wormer e.g. Equest Pramox, or Equimax
  2. Thereafter horses should have regular FWECs. The interval can increase in yards with
    a track record of low burdens. N.B. All horses in a yard should be tested , as they may
    have widely varying worm burdens, due to differing levels of immunity to worms.
  3. All horses should be wormed in the late autumn with Pramox to remove bots,
    tapeworms and any adult roundworms and Redworm including the encysted stages.
  4. For many horses once a year worming will be sufficient. Horses identified with higher
    worm burdens will need to be wormed more frequently.