Horses grazing

Worm control

Worming Programme

A general management guide to reduce wormer resistance:

  • Good field management is very important – poo pick your fields daily
  • Where possible rotate the fields with other species such as cows/sheep. Worms are species dependant, so rotating the field on a cycle of 6 weeks will break the worm life cycle.
  • If possible, rest the fields for a period of time (6 months), try to have winter and summer fields
  • Do not over graze fields and try to keep stocking density low
  • Worm 3 days before moving horses to a rested paddock to minimise contamination
  • Worm new arrivals and keep stabled for 72 hrs as treated horses are likely to shed more eggs in this period. Having stabled will reduce potential for contamination of pasture.


A worming programme for an adult horse (over 2 years old):


  • Worm egg count (WEC) test for other intestinal worms

+ve: treat with ivermectin (Eraquell) and wait one month for next WEC

-ve: wait three months until the next WEC June


  • Worm egg count (WEC) test for other intestinal worms

+ve: treat with ivermectin (Eraquell) and wait one month for next WEC

-ve: wait three months until the next WEC September


  • Worm egg count (WEC) test for other intestinal worms

+ve: treat with ivermectin (Eraquell) and wait one month for next WEC

-ve: wait until the next WEC March

Mid November

  • Saliva test for tapeworm

+ve: treat with moxidectin & praziquantel (Equest Pramox) and repeat saliva test in March (to treat encysted redworm & tapeworm)

-ve: treat with moxidectin (Equest) to treat encysted redworm in December.

  • Worm egg count (WEC) test for other intestinal worms – if required


How to take a Worm Egg Count sample:

  • Take a small sample, ideally one handful no more than 12 hours old – from three different droppings. All the faeces collected for the sample should be gently mixed and put in the same sample bag.
  • The sample should be closed and kept refrigerated, unless it can be delivered in the next few hours to the practice.
  • Label the bag clearly with your name, the horses name and the date taken.
  • The sample MUST NOT be posted or kept in the car under high temperatures.

Our wormers are competitively priced – cheaper than most online prices.

For further advice please do not hesitate to contact us 01344 426066.


Worms in Horses

Almost all horses will have some worms in their intestines and most of the time these do not cause any symptoms. Some horses will naturally have better immunity to worms and therefore it is common to find that 80% of the worms are in only 20% of the horses within the herd. By using worm egg counts throughout your grazing season you can identify these ‘high shedders’ and by treating these individuals you will help protect the whole herd. This approach is known as strategic worming and helps protect important drugs from developing resistance as well as save money overall.

Strongyles are the most common worms in horses and are broadly split into large and small strongyles.

Large strongyles can cause significant bleeding and damage by migrating through the intestine wall through the blood vessels of the guts. Clinical manifestation can be rapid weight loss, diarrhoea and surgical colic. Faecal worm egg count throughout the grazing season (approximately every 3 months) is recommended to detect the level of infection.

Small strongyles (cyasthostomes) larvaes hibernating within cysts created in the gut wall over the winter. Once the weather warms up, the larvae (immature worms) emerge in large numbers which damages the intestines and can lead to severe diarrhoea, colic and potentially life threatening condition. When the larvae encyst within the gut wall they don’t lay any eggs, this means horses could have encysted red worms with a negative worm egg count. We strongly recommend worming with a Moxidectin based wormer (Equest) in December.

Ascarids are primarily affecting foals and young stock. The adult ascarids can grow up to 50 cm long and obstruct the intestines leading to weight loss and colic. The larvae can migrate through the gut to the liver or lungs, causing respiratory signs such as coughing or nasal discharge. As horses age they develop immunity. Ascarids are detected by worm egg count.

Tapeworms cluster together at the junction between the small and large intestine obstructing the intestine, hindering the horse’s ability to absorb the nutrients in its diet and can lead to colic. Tapeworm eggs are ingested by its intermediate host (forage mite). Re-infection happens when horses eat infected forage mites. Tapeworms can reliably detected throughout a blood sample or saliva test.

Lungworms are key if horses are sharing fields with donkeys or have in the past. Donkeys are the natural host of lungworms. In horses it can cause persistent cough and respiratory signs. Lungworm can be detected via a tracheal wash or by a sedimentation test on the faeces.

Bots (Gastrophilus) are typically noticed during the summer grazing season. Bot flies lay their yellow eggs on the horse’s legs and as the horse grooms itself, it ingests the eggs which hatch into larvae and sit in horse’s stomach. Once in the stomach they are typically of no significance to the horse and are naturally excreted by the horse without any treatment being required.

Pinworms (Oxyuris equi) can cause irritation in the rectal mucosa and itchiness around the tail and anus as larvae feed on the mucous lining in the intestine. Test for pinworms include examination of the faecal sample or applying sellotape to the skin around the back passage and then viewing the tape under a microscope to identify presence of eggs.


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