By Dr Colin Walker  BSc, BVSc, MRCVS, MACVSc (Avian health)

Parasites of concern in poultry are roundworm, hairworm and tapeworm, Coccidia and lice and mites.
Worms are extremely common, particularly in free-range poultry. Being a primary parasite, they drain the birds of nutrition, causing ill-thrift, a general failure to thrive, a vulnerability to other diseases, and, in severe infections, death. Both roundworm and hairworm have what is called a direct life cycle in that the eggs are passed in the droppings and after a period of time in the environment, become infective. New birds become infected by inadvertently eating these eggs while feeding, drinking or scratching around their yard. Once an egg is swallowed, it hatches and eventually matures into a new worm in the bird’s bowel.

In roundworms, the life cycle is particularly short, being only 21 days. This means that if a chicken is wormed and swallows an infective egg the very next day, in only 3 weeks that chicken will have mature roundworms in its bowel again. To completely eradicate roundworms from a flock involves worming the birds every 3 weeks and each time following up with a particularly thorough clean of the yard. Ongoing hygiene is particularly important because any dropping passed prior to worming will contain worm eggs that have the potential to reinfect the chicken. Often in a free-range situation, no matter how thoroughly one cleans, it is not possible to completely remove every piece of dropping and so some reinfection does occur. In this situation, regular worming is done, not so much to eradicate any parasites but rather to keep them at a low level where they are not causing clinical disease. Often here, in a yard that is basically clean, worming every 3 months will provide adequate control. There are many medications on the market to worm birds, but the one I recommend is Moxidectin. It provides good clearance of roundworms and hairworms, is very safe and easy to administer, and has the handy side effect of killing any external parasites that feed off body fluids. This includes all mites. The dose of Moxidectin 2 mg/ml for the flock is 5 ml to 1 litre of water for 24 hours. This dose is based on normal water consumption. If for one reason or another the birds’ water intake on that day is low, the drug is safe enough to provide for a second or a third day to ensure that all birds receive an adequate amount. If some birds receive a double or triple dose, this will do them no harm. It is important that the water containing the Moxidectin is mixed freshly each day, however, and that, of course, no other water sources are available. Moxidectin can also be given to individual birds at the dose of ½ ml per kg as a single dose orally.

Tapeworms have a more involved life cycle. The adults, which live in the bowel, pass packets of eggs in the droppings that need to be eaten by an insect to become infective. Chickens can only become infected by eating insects carrying the tapeworm larvae. It is often possible to tell if a chicken is infected by tapeworms simply by looking at the droppings. Tapeworm egg packets are visible to the naked eye and appear as white pellets stuck in the droppings. Most are about the size of a grain of rice but bigger and smaller types occur and sometimes rows of egg packets can be passed together, which appear as white ribbons in the dropping. The only way to reliably tell if a chicken has roundworms or hairwoms is through a microscopic examination of the dropping. The usual drug used to treat tapeworms is Praziquantel. This is available in a variety of tablets and syrups. I usually use the brand Prazivet, which is added to the water at the rate of 5 ml to 1 litre for 24 hours. Like Moxidectin, an individual bird can be treated with Prazivet by giving ½ ml of the neat solution per kilogram of body weight as a single dose.

Coccidia are protozoan organisms that live in the lining of the bowel. Infected birds are usually lethargic, underweight and have diarrhoea that can be blood tinged. The Coccidia eggs are released in the droppings and fresh chickens become infected by inadvertent ingestion of grain or water contaminated with these droppings. In a free-range situation, most chickens have a low-level ongoing exposure to Coccidia. Rather than make them sick, this stimulates the development of a strong natural immunity that keeps them healthy. Chickens become unwell with Coccidia in one of several situations, for example, where they are housed in dirty damp conditions that provide a high level of exposure to the organism, or where they become run down generally, in which case the Coccidia will multiply and cause disease. Alternatively, if chickens which have a low natural immunity to Coccidia suddenly come in contact with even moderate levels, then disease can occur. Coccidia is diagnosed through microscopic examination of a dropping sample. Often where Coccidia is diagnosed, it is important to review the general management and housing as flaws will often be found here. The drug I recommend to treat Coccidia is Baycox. This is used at the rate of 3 ml to 1 litre of water for 48 hours. Where a flock is having an ongoing problem, this treatment is usually repeated every 4 - 6 weeks until the birds develop a stronger natural immunity to this parasite, while all the time ensuring that the birds are generally well cared for and that their pen is kept clean and dry.

The two main external parasites of chickens are lice and mites. Red mite, in particular, seems ubiquitous in chickens and is a common cause of failure to thrive. Severe infections will kill, particularly young chickens due to anaemia and it is vital that management protocols are in place. Lice live off feather debris and cannot survive off the chicken. Mites, on the other hand, feed off body fluids and survive well in the environment. Only a small number of the mites infecting a chicken are found on the bird at any one time. Many live in the nooks and crannies around the pen. To treat lice is a simple matter. As they cannot survive off the bird, it is simply a matter of dipping all of the birds. Mites can be removed also by dipping, however, as mentioned earlier, Moxidectin can be used in the birds’ drinking water to kill mites on the bird at that time. With mite infestation, however, it is vital to also treat the pen at the same time otherwise reinfection quickly occurs. When treating the pen, it is scraped and cleaned out as normal but then an insecticide is misted onto the scraped surfaces and into the nooks and crannies. This is usually done on the morning of a warm day and when the pen is dry after a few hours, the birds are readmitted. The recommended insecticidal spray is Permethrin. This is available in a number of preparations but I find it easiest to use as a water-soluble liquid where it is diluted 10 - 20 ml/l. Permethrin is also the dip of choice in chickens. To prepare the dip, add the Permethrin at the same rate of 10 - 20 ml per litre of water and add also a wetting agent such as baby shampoo or a few shavings off a bar of soap. Ensure that the water is warm and dip the birds in the morning of a warm day so that they have a chance to dry before nightfall.


Moxidectin 2 mg/ml, 5 ml per litre of water for 24 hours every 3 months
Monitor the droppings for tapeworm segments and if observed give Prazivet 5 ml per litre of water for 24 hours.
If Coccidia is a problem, give Baycox 3 ml to 1 litre of water for 48 hours every 4 weeks as required
Dip all birds in Permethrin and any new introduced bird. Ensure that the pen is sprayed simultaneously.

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