Back garden chickens are very susceptible to worms. Poultry vet Victoria Roberts offers her expert advice.

Chickens that go outdoors are always exposed to internal parasites because these are carried by insects and earthworms, both of which are favourite snacks for chickens. If chickens have a heavy worm burden, it weakens them, making it easier for bacterial or viral diseases to take hold.

How common?

Very common due to the chicken lifestyle. Wild birds also transmit internal parasites.


A change in behaviour (which can be subtle) is often the first sign. Later, hens will hunch up, close their eyes to conserve energy and feeding will slow or stop. Weight loss can only be discovered by regular handling.

Types of worms

1. Gapeworm: lives in the trachea of a bird and when eggs are laid, they are coughed up and excreted to infect the next chicken. Chickens can gasp/cough with throat extended.

2. Capillaria: these tiny worms, also known as hair worm, live in the intestine. They quickly cause ill thrift and can be fatal if not treated.

3. Heterakis: lives entirely in the caeca (two blind-ended parts of the large intestine where some fermentation of plants occurs). It causes ill thrift but is the vector for histomonas (see below).

4. Ascarids: also known as roundworms, these live in the small intestine. If there are many of them they can impact, and this is fatal.

5. Trichostrongyles: live in the intestine and cause severe weight loss.

6. Tapeworm: live in the intestine, cause weight loss and can be fatal.

7. Gizzard worm: live in the gizzard and can be fatal in young stock.


Flubenvet is the best licensed product as it treats all types of worms (a new soluble product only treats roundworms). Use 60g powder to 20kg feed for seven days, or for a few hens use 3g in 1kg feed for seven days. Add a small amount of vegetable oil first to pellets to stick the powder. Use at least before the breeding season and possibly every two months or less, depending on stocking density and ranging area. There is no resistance to Flubenvet and no egg withdrawal at this dose rate. Feed can be bought with Flubenvet in it, if preferred.


Regular use (prophylactic) of a licensed product should avoid the situation where a bird is so infected with worms that either impaction results, or when a large burden of worms is killed, the toxins they release kill the bird. Stress can alter the delicate balance and allow intestinal worms to proliferate. Heavily grazed or stocked poultry areas should be rotated to avoid a build up of internal parasites.


Very good if treated regularly.


Other internal parasites…


Histomonas is a protozoa (single-celled, free-living organisms) affecting the liver in chickens, turkeys, pheasants, quail, peacocks and guinea fowl. Bright yellow diarrhoea is a symptom, plus lethargy; the disease is also known as blackhead. The intermediate host of these protozoa is the heterakis intestinal worm carried by chickens (see above), thus if hens are wormed regularly, then the incidence of blackhead is much reduced.


Hexamita is a protozoa normally found in the gut but it can cause diarrhoea and unthriftiness in chickens, turkey and pheasant poults. The treatment is the same as for histomonosis.


Trichomonas, another protozoa, causes an oral canker in hens. A pale yellow cheesy substance appears in the mouth and throat. New purchases should always be checked for this condition by opening the mouth. Maintain vitamin A levels in winter with dark green vegetables to help prevent this.

Veterinary treatment only.

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