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Are Worms in Horses Bad for their Health?

Intestinal worms in horses is a very common health concern with all horses being at risk. These internal parasites can cause a number of different health issues from mild to quite severe, depending on the extent of the worm burden the horse is suffering from. Signs of a intestinal worms can include;

In Mild Burdens
* Failure to thrive
* Weight loss
* Poor, rough or dull coat
* Rubbing/itchy backside
* Decreased appetite

Developing to more severe cases
* Pale gums
* Anaemia
* Bouts of colic
* Diarrhoea
* Pneumonia
* Emaciation
* Severe gut issues like torsion, perforation or thrombosis
* Death

There are over 20 different intestinal worms that can be found in horses, the most common worms of concern for the horse population today are;
Large strongyles also known as redworms feed on blood, causing anaemia. They migrate through the intestinal wall into blood vessels and arteries where they can cause blockages.
Small strongyles or small redworms bite the the lining of the intestine, then feed on blood causing anaemia.
Roundworms sit in the gut and absorb nutrients, and if enough of them cause obstructions. Young roundworms live part of the lifecycle in the lungs and can cause damage to the lung and windpipe particularly in young horses.
Tapeworms attach to the gut lining, sucking and absorbing nutrients from the bowel . They cause irritation, thickening, inflammation and ulceration to the gut wall and in large numbers can cause blockages.

Roundworms in horses. Image from the "Know Your Worms" feature on their website.
Roundworms. Image courtesy of Virbac Animal Health “Know Your Worms”


Controlling intestinal worms in horses is generally an easy process with the use of anthelmintics (wormers). There are a number of products available but it is important to understand that all effective products will consist of one or a combination of four different active ingredients (chemicals) in different combinations in order to control a variety of worms. The four main chemical groups that are used to treat worms in horses are; Macrocyclic lactones (mectin based) – broad spectrum protection (not tapeworms)
Benzimidazoles – generally used for rotation worming
Praziquantel – specifically for tapeworm control
Tetrahydropyrimides – narrow spectrum wormer
Different products may be formulated using one or a combination of these ingredients and developed into liquids, gels, pastes or granules.

Controlling worms is essential for the health of your horse. The best way to do this is using a combination of a number of methods including;
* Regular and appropriate worming program including a rotational wormer (changing the active ingredients used)
* Paddock management and hygiene, ie rotating paddocks, allowing rest periods, picking up faeces and managing pasture.
* Doing faecal egg counts to determine if worms are present or being controlled.

For more advice on worming your horses please contact the vet-n-pet DIRECT trained vet nurses or your veterinarian will be able to help.

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