21 May 2018 | Online since 2003

17 February 2009

Worms - The hidden enemy

Capilliaria (hairworm) egg under the microscope - note thick outer wall making egg resistance to drying, cleaning and disinfestants

We make no apologies for raising the topic of worms again in this month’s article.

In the past year, we have seen an increasing number of health and production problems in free range flocks associated with heavy worm burdens.

When producers see drops in production or increased mortality in a flock, their first thought may be of Infectious Bronchitis or other disease challenge but in fact worms are a common and often overlooked reason for poor flock health and/or poor production.

Massive ascarid (roundworm) burden blocking the small intestine of a laying hen

We suspect that part of the reason for the increase in worm problems seen is the milder weather over the past few years (although as we are writing this, the snow is falling outside!). In particular, the very wet Summer and Autumn seen in 2008 may have contributed to the increase in worm populations.

Another reason for the apparent increase in worm problems is a build up of worm eggs on pasture in free range operations which have now been running for a number of years and in some cases have not been observing a good system of paddock rotation.

Large numbers of ascarid worms (roundworms) blocking a loop of small intestine from a laying hen

Historically, worm problems were thought to be somewhat seasonal in that worms begin to thrive on pasture once the ambient temperature stays consistently over 10 degrees but increasingly we are seeing worms as more of an all year round phenomenon.

The worm problem
What sort of problems can worms cause in my birds?

• Worm infections cause damage to the birds’ gut. This gut damage can lead to a number of problems with health and production including poor body weight gain or loss of condition.

• Affected birds may show pale or droopy combs, some unevenness may be seen in the flock and birds may appear generally unthrifty.

• Poor feed conversion.
• Increased risk of egg peritonitis.

• Increased risk of secondary gut problems, for example, bacterial infections and Brachyspira.

• Problems with egg quality, in particular loss of shell colour and strength. Reduced egg size and sometimes pale yolks.

• Increased risk of cannibalism through vent pecking due to straining.

• In very high infestations, mortality in the flock may be increased.

In chickens there are three main types of worm which may cause problems in free range birds. These all affect the intestine with roundworms and hairworms affecting the duodenum and small intestine, hetarakis worms in the caeca.

Roundworms (Ascaridia galli)
These are the largest of the chicken intestinal worms and are the most common. Worms are white with adult worms up to 2 inches long, worms may be visible in droppings in heavy infections.

Hairworms (Capillaria)
Hairworms, as their name suggests, are small and barely visible to the naked eye. These worms are capable of causing severe damage to the intestine where present in small numbers. Hairworm infection can be identified by examining faecal material under the microscope or looking at intestinal material from birds submitted for post mortem.

Caecal worms (Hetarakis gallinarum)
Hetarakis worms spend most of their time in the caeca. The worms themselves often cause no obvious problem but their significance is that they can carry another parasite (Histomonas) into the bird. Histomonas is the cause of Blackhead which has been discussed in previous Ranger articles. Blackhead can cause significant mortality in free range flocks so it is important to control the caecal worm to reduce the risk of Histomoniasis.

There is no treatment for Histomoniasis so control of the problem is based on preventive measures such as regular worming.

How do birds become infected with worms?

Chickens become infected with worms by picking up worm eggs from their surroundings. This may be from within the shed from the litter area or from other surfaces or from soil, grass or faecal material on the range. Worm eggs are extremely resistant to disinfectants and it is probably not widely recognised by many free range producers that the normal terminal cleaning and disinfection programme used in poultry houses would not be fully effective in removing worm eggs from the environment. Thus a new flock of pullets may be exposed to worm eggs as soon as they arrive in the house and before they are let out onto pasture. Obviously the risk of exposure to worm eggs on pasture is greater.

Worm eggs need warm moist conditions to develop outside the bird which is why historically worm problems are frequently worse in the Spring and Summer particularly if the weather has been wet.

What can the producer do to control worms?

It is important to agree an appropriate testing programme for your flock with your veterinary surgeon. Waiting until you see worms in the droppings is too late! There is no one worming programme which will be appropriate for all farms so it is important to discuss the risk factors and previous history of your flocks with your vet to decide which is the most appropriate testing programme for you.

There are two main ways of testing flocks:

a) Looking at faecal samples (droppings). This is a relatively inexpensive and quick way to monitor levels of worm eggs in your flock. However the weakness of this testing method particularly on farms where there is a history of previous worm problems is that the test is picking up worm eggs and so early worm infections may be missed as there are not adult worms in the gut producing eggs which can be detected by faecal examination.

b) Examination of cull or dead birds from the flock. This is a useful tool to use alongside the routine faecal examinations as it allows your veterinary surgeon to examine the birds’ intestine for evidence of worms and also to check general gut health.
What can I do to control worms in my free range flock?

• Regular worming, timings based on previous experience and discussion with your veterinary surgeon as to the most appropriate programme. On farms where there is a severe problem with worms, this may mean worming as frequently as every 4-5 weeks.

• Good paddock rotation to reduce worm build up and reduce the risk of land becoming fowl sick. If you are using a regular worming programme, try to time the worming so that the flock are wormed just before they move to the next paddock in the rotation.

• Ensure land is well drained if possible. Additional drainage work may be needed on very heavy land.

• Restrict birds’ access, as far as possible, to any poached or muddy areas.

• The area closest to the house is always a high risk area for build up of worms and other pathogens. Use stones in the area close to the popholes near the house to help keep birds’ feet clean and allow dropping passed there to dry and to be broken up and exposed to ultra violet sunlight which helps to kill the worm eggs.

• Keep pasture short especially close to the houses again to allow uv light access to droppings.

• Carrying out regularly worm egg counts on faeces (20-30 fresh droppings taken from slats).

• Submit cull or dead birds for post mortem at peak, mid and/or end of lay to check worm burdens and general gut health.

What should I use to worm my birds?

At present there are two products licenced for use in chickens in the UK (these contain the same active ingredient, Flubendazole). Flubenvet can be used in feed and Solubenol in drinking water. Both products are licenced for use in laying flocks with a nil egg withdrawal period. (Organic flocks will require egg withdrawal period if these products are used).

You should discuss with your veterinary surgeon which is the best product to use for routine worming of your flocks.
The advantage of the water soluble product is that if a worm infection is diagnosed in your flock and you have just had a feed delivery, then the flock can still be wormed promptly without having to wait for the feed bin to be emptied so you can refill with feed containing a wormer. There is also the flexibility to treat a specific house rather than treating the whole site.

Why do we still see problems with worms in flocks despite knowing how to control them?

Problems are seen, we think, because producers under-estimate the damage that worms can do to health and production. Generally you can’t see worms so they tend to be a hidden menace. Worming is expensive and so it may be tempting to cut corners on the worming programme – but in many cases where worms have caused severe production problems, cost of regular worming would be small compared to the cost of lost eggs.

In summary, make sure that you know the worm risk on your farm and include a robust worm monitoring and control strategy in your veterinary health plan.

For effective worm control, the producer needs to be one step ahead of the worms. We are lucky in the UK that we have effective and safe products to control worms in our laying flocks and, at present, no problems with parasite resistance to wormers as is the case with some other farm livestock.

There is no excuse for worm problems in the modern laying flock.

C.I.F.Knott, BVM & S, MRCVS
S.A.Lister, BSc, B.Vet.Med, CertPMP, MRCVS
Philip Hammond, BVetMed, MRCVS


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