With winters in the UK becoming increasingly warm and wet, it is becoming ever-more important to stay on top of worms on poultry farms.

Intestinal worms of poultry thrive in mild, damp conditions, and if left unchecked can have severe consequences for poultry farmers, according to poultry vet Sam Northing, of Avivets.

“There are several species of worms that can affect domestic poultry and game, and they can result in reduced productivity, sick birds and even disease transmission,” he explains.


Worm eggs can become infective within 1-2 weeks of being excreted by birds, dependent on temperature, and remain so for years in ideal conditions; warm, wet soil shaded from direct sunlight.

Worms can cause a broad range of issues for commercial layer, broiler and turkey producers.

At their most mild, lower productivity can be observed. More severe infections can cause a range of health issues, and they can also cause internal damage and inflammation that allows bacteria to invade the body to cause problems, such as peritonitis, a common cause of mortality in laying hens.


And every farm is at risk – even brand-new free-range egg units will often gain some degree of worm infestation as wild birds, or rodents introduce them to pasture.

They can also be introduced onto farms via contaminated clothing or footwear, highlighting the importance of good biosecurity.

How do they spread through a flock?

Birds pick up worm eggs or larvae while foraging, and the problem is most common in free-range flocks.

Once ingested, the worms will mature into adult worms before producing eggs, which pass from the bird through its faeces.

As these cycles repeat, worm burden in the environment and ultimately in the birds grow until the population is sufficient to cause health problems in poultry, according to Mr Northing.

That can take a surprisingly short time. “The life cycles of the various worm species occur in just a matter of weeks but, depending on the species, can be as little as 18 days (Gapeworm).

“Once worms are present on farm, they can build up quickly and need constant monitoring and treatment to bring them under control,” he adds.

How do you know a flock has worms?

Different species of worms (see below, species that affect poultry) can cause various symptoms and signs of infection.

There may be overt signs that a flock is infested such as an egg drop, reduction in egg quality, loss of bird condition or diarrhoea.

Equally, there can be subclinical infestations. “That means the problem can be hard to see but is negatively effecting birds’ performance.”

“It’s therefore important to be proactive with worm control,” Mr Northing says.

Post-mortem examinations undertaken by a vet will uncover most common worm species – although Capillaria red worms can be hard to see with the naked eye.

Taking worm-egg counts (WECs) on faecal samples is a less invasive way of monitoring for the presence of mature worms.

Regular counts, most commonly every six-to-eight weeks, will give information about the presence of worm species and numbers in any given flock, and give farmers the knowledge they need to make an informed decision about control.

Counts must be done often, because young worms that are present in the bird but not yet mature will not produce eggs, therefore causing a false-negative test result.

But these will be picked up in the next WEC test, so it is essential not to miss a test or leave it too long between tests.

What control methods are there?

The most responsible, and economical approach, according to Mr Northing, is to react to positive test results with treatment when necessary.

While there is no reported resistance to wormers in poultry, it is prudent to target interventions based on test results.

The alternative is to treat regularly to keep worm levels low. This should be done under veterinary guidance. Treatments every 6-8 weeks will often be very cost-effective in flocks/housing with an established worm burden.

Treatments can be administered through feed or water. Flubendazole and fenbendazole are two examples of active ingredients from the same family of wormers.

Vet-prescribed products will tend to be delivered via water, while products available from a vet or a ‘suitably qualified person’ are more usually milled into feed rations.

Following a course of treatment, it is advisable to follow up with a worm-egg count to assess its effectiveness.

Top tips for keeping worms under control

  • Good biosecurity is critical for poultry health, and it’s no different for controlling worm populations.
  • While general biosecurity is essential, both ensuring footwear is changed where appropriate and proper foot dip management are particularly helpful.
  • Think about drainage on the range; puddles are especially risky sources of worm eggs if birds are drinking from them, and wet grass in warm conditions can be a haven for worm egg development
  • Stones near pop holes will also help with drainage and can help to clean birds’ feet as they return to the shed
  • Keep grass short. UV light from the sun can kill both worm eggs and larvae
  • Rotate paddocks where possible to prevent populations from building up
  • Ensure cleaning and disinfection at turnaround is performed effectively. There are disinfectant products available that can kill worm eggs when applied correctly.

Worm species that affect poultry

The most common poultry worms are:

  • Capillaria Hairworms – can cause significant damage even in minor infestations. These are intestinal worms, hard to see with the naked eye, that can cause severe symptoms such as diarrhoea, weight loss and a drop in egg production.
  • Caecal worms – Heterakis gallinarum, usually found in the caecum. They are a problem because they are a host in the lifecycle of the potentially fatal Blackhead Disease (Histomoniasis) which is a particular problem of turkeys but can also affect chickens.
  • Roundworms – Ascaridia, these are larger intestinal worms which are evident in post-mortem examinations. In severe infestations, they can cause diarrhoea, reduced productivity and loss of condition.
  • Gapeworm – Syngamus trachea. A species of worm which resides in the windpipe causing respiratory distress known as ‘gaping’. Severe infestations can cause suffocation. This is a common problem in game birds.