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Worms in Free-Range Hens

06 January 2009

Claire Knott, Stephen Lister and Philip Hammond, partners in Crowshall Veterinary Services in the UK, describe the most common worms in free-range poultry and how they can be controlled.


Claire Knott, BVM&S MRCVS

Stephen Lister, BSc BvetMed Cert PMP MRCVS

Philip Hammond, BVetMed MRCVS

Whenever your birds have contact with their own droppings, there is a likelihood of exposure to intestinal worms. The infection starts with eggs voided in droppings and then picked up by birds eating or foraging in anything contaminated with such droppings, those eggs hatching and maturing into adults ready to lay eggs to pass out in the droppings again. Whether they then cause problems in your birds depends on the balance between challenge and control.

Answering some of the following questions will help push the balance in favour of your birds.

What can worms do to my birds?

Worm infections cause damage to the bird's gut. This may result in a variety of problems including:
  • Loss of shell colour and strength, yolk colour and egg size
  • Poor body weight gain leading to unevenness or sick birds. Affected birds may be dull and show pale combs.
  • Poor feed conversion
  • Increased cannibalism through vent pecking due to straining
  • Increased risk of egg peritonitis
  • Death, in very heavy infestations.

Which worms should I be worried about?

There are three main worms that may cause problems in free-range birds:
  1. Roundworms (Ascaridia)
    These are the biggest and the most common. They are white, up to 5cm long and may be visible in droppings in heavy infestations.
  2. Hairworms (Capillaria)
    These are much smaller (hair-like) and barely visible to the naked eye but can cause significant damage, even in moderate infestations.
  3. Caecal worms (Hetarakis)
    As their name suggests, these worms spend most of their time in the lower end of the gut, the caeca. Frequently, the cause no obvious harm in themselves but they can carry another parasite, Histomonas, into the bird. Histomonas is the cause of blackhead, and hence control of one parasite can help to control another. With the increasing incidence of histomoniasis &ndash' for which there is currently no treatment – the role of regular worming is even more important.

How do birds become infected?

Birds become infected by picking up worm eggs from grass, soil or faeces. The worm eggs need warm, moist conditions to develop outside the bird, which is why problems are frequently worse in the spring and summer, especially following a wet spring.

If we know all these answers, why does worm control so 'hit-and-miss'?

The answer probably lies in the fact that we do not spend enough time thinking about how the problem affects specific sites.

  1. Worm are common and almost inevitable in laying flocks unless birds are effectively wormed before moving to laying accommodation and having the luxury of moving to 'virgin' pasture.
  2. Worming prior to the onset of lay with the only licensed wormer means that production should at least start on with a clean slate.
  3. Worms can build up quickly on the laying site and can peak at a time when birds are reaching their peak production.
  4. Worming in lay can remove the offending worm burden.
  5. Worming only once during lay may not prevent worms for the pasture re-infecting birds and building up to significant levels, suggesting repeated worming may be necessary.

So how does this affect me on my farm?

If you have to ask this question, then the answer is that you need to start looking!

Undoubtedly, some producers have been in business for many years and have never identified a problem. This may be due to a combination of the the fact hat your pullet rearer has delivered you a clean flock and either by good management, pasture rotation, soil type and drainage or good old-fashioned luck, your birds have not met a challenge during lay. Alternatively, your birds may have met a moderate worm burden, which has not had a significant effect on performance. Or you just have not noticed!

How do I know if my birds are carrying worms?

Worm burdens can be most easily identified by examination of droppings for the presence of visible roundworms although this will not help for hairworms, which can be more severe in their damage to bird performance but are too small to see.

Sending droppings samples to your veterinarian gives a more informative answer. Twenty fresh samples taken from the floor slats is a good sample.

A better strategy is to submit ailing, thin or other culled birds to your veterinarian for a routine post mortem examination and health screening, when visible and microscopic tests on the gut can be done. This often picks up a burden before it become patent, i.e. when birds are pushing out large numbers of eggs that could be detected in a droppings sample.

When should I test my birds?

It is a good idea to test your birds via their droppings soon after arrival on site to check they are worm-free before they start to lay. After that, it is worth establishing a programme with your veterinarian. Clearly, if you experience a drop in production, loss of egg size or shell colour, you should follow this up with a droppings sample and sick or recently dead birds.

Even if no specific problems are experienced, peak worm egg output tends to coincide with peak egg production by the hens. So a sample taken then, proving negative, gives confidence that there is nothing wrong.

A sample late in the life of the flock also gives a benchmark for your worm control strategy, and lets you know the likely status of that paddock for the next flock.

Armed with this information, you are either comforted that all is well, or you may uncover a lurking menace. At least with latter case, you know what you are dealing with and can do something about it.

What does all this tell me about how to control worms in my flock?

Consider some or all of the following actions:

  • Regular worming on the basis of previous experience and discussion with your veterinarian.
  • Effective paddock rotation to reduce worm build-up, and put off land becoming 'fowl sick'.
  • Use well drained land - or try to improve the drainage.
  • Avoid access to poached, muddy areas that encourage worms (and other pathogens).
  • Use stones in the area close to the pop-holes to help clean the birds' feet and allow droppings passed there to dry, break up and be exposed to ultraviolet sunlight, which is lethal to worms.
  • Keep pasture cut short, especially close to the houses, again to allow sunlight access to droppings.
  • Regular worm egg counts to monitor the success of your chosen strategy.
  • Submit birds for post mortem at peak, mid and/or end of lay to check the worm burden.

Armed with this information, you can develop a worming strategy and pasture management that suit your specific enterprise and conditions, and helps to avoid pasture problems before they affect your flock – and your pocket.

Further Reading

- You can contact Crowshall Veterinary Services by clicking here.


December 2008



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