Tower Equine

Veterinary Surgeons


A Targeted Approach to Worming - March 2014

Print PDF

The Problem

Gastro-intestinal parasites (worms) are ever present in the UK horse and pony population. Since the 1960’s we have relied on the use of ‘wormers’ to try to manage these but the recent scientific evidence suggests; that by treating all horses the same, worming every 8-12 weeks and rotating the types of wormer used we are actually becoming less effective at managing worms. There are 2 main reasons for this…………………

1) Over the years the types and numbers of the different roundworms found in the intestine have changed, but we are still using the same management programmes. 40 years ago the large strongyle caused the majority of problems in the UK (traditional worming programmes were designed to reduce the presence of large strongyles and have been effective in doing this) but the predominant roundworm species now found in adult horses are the cyathostomes (small strongyles). In addition Parascaris equorum and Strongyloides westeri are also commonly found in young horses. The tapeworm (Anoplocephala perfoliata) can be found in adult and young horses.

2) The high levels of use of wormers have led to widespread resistance to some of the types of wormer used and they are no longer as effective at killing the worms.

Because of this, the way in which we are now approaching the management of worms is changing. In the past there was a belief that with the use of wormers we could effectively eliminate these worms; however we have realised that this is not possible. We also know that at low levels, some of these worms do not cause clinical problems in adult horses and can actually be beneficial in stimulating the development of the horse’s immunity (this has been termed ‘parasite refugia’). In addition we cannot continue to rely as heavily on the use of wormers because of the growing problem of resistance.

We know that within a population of horses there will be only a small number of horses that harbour the majority of the worms (20-30% of the horses will have 80% of the worms). Yards in which the paddocks are well managed (where the droppings are removed at least twice weekly) will also have lower levels of worms on the pasture.

The Solution – Targeted Worming

The solution to this is a targeted approach to worming: we identify those horses that do require worming and then treat those individuals with a wormer that will be effective for the type of worm involved. We can also then test that the wormer has been effective (and that the worms are not resistant to it).

For each horse we test the droppings and perform a worm egg count (WEC) which gives us an indication of whether there are adult female worms in the intestine and whether treatment is required. This test can detect tapeworm eggs but is not 100% reliable, so our programme advises worming once a year to kill tapeworm. We then advise you whether your horse requires worming and which wormer to use. As your veterinary practice we can also take in to account any other relevant information about your horse’s health before giving specific advice.

The targeted worming approach is fairly simple: we advise that adult horses (over the age of 5) on well managed pasture are tested 3 times per year, and that all horses are wormed once each year for roundworm and tapeworm (either a wormer containing ivermectin+praziquantel or a double dose of pyrantel).


Time of Year

Targeted Worming Plan


Worm Egg Count (WEC)


Worm Egg Count (WEC)


Worm Egg Count (WEC)


Worm for Roundworm and Tapeworm


For the adult horses that test positive for the presence of egg laying female worms we advise that the horse is wormed either with ivermectin or pyrantel (see the table below for wormer types and trade names). We can then perform a second test 14-17 days after you have given the wormer (called a ‘faecal egg count reduction test’) to test for resistance (this is not necessary every time). Please note we are trying to limit the use of moxidectin for cases when we need it specifically to reduce the development of resistance.

We know that young horses (4 years and under) are more susceptible to gastro-intestinal worms, partly because they have not built up sufficient immunity. For this reason they are not suited to an entirely targeted approach but a combination of strategic and targeted worming can be used. Please contact us about your young stock and we can discuss your specific needs and circumstances.


Wormer Group

Wormer Name

Trade Name Examples

UK Resistance Levels




Panacur/ Panacur Equine Guard









Eqvalan/ Vectin/ Eraquell

(+Praziquantel) Eqvalan Duo/ Equimax


(+Praziquantel) Equest Pramox







What is Involved

We can provide you with collection kits: collect a small handful of fresh faeces; follow the instructions provided and fill out the attached forms. You will need 1 kit per horse. You will then need to bring or post the sample to Tower Equine. We will then email you with the results and worming advice.

The Tower Equine worm egg count costs £9.50 (inc VAT), in the majority of cases this is more cost effective than worming your horse. The targeted approach will ensure you are only treating your horse if needed and we can test that the specific wormer you have used is effective.


Alice K Brown