ID 63799023 © C Gabi |

There are hundreds of different diseases that can affect poultry, and free-range chickens may be more or less at risk.  If they are farmed well, they are much less likely to get many of the infectious diseases that can be a problem in intensively housed birds.  But they may be more at risk of other types of disease and in particular parasitism because many types of parasites lay eggs that are passed in the droppings to infect other chickens when they forage.

Although the types of disease that can occur vary hugely from one region to another, there are certain infectious diseases that are relatively common practically everywhere.  In this article, we’ll look at some of the most common parasite diseases.

It’s worth noting that almost all the internal and external parasites of birds tend to be most severe in birds that are in poor body condition, and the parasites themselves cause loss of body condition.  So infestation usually means a downward spiral, unless it is tackled early.

Diseases caused by parasites


This disease is caused by a tiny one-celled parasite in the intestine.  It is a common disease of young birds up to 6 months of age and it causes dullness, bloody diarrhoea, weight loss and eventually death.  Keeping the bedding clean and dry will help control this disease, as wet bedding is one of the predisposing factors.

Birds usually develop resistance to coccidiosis as they get older, and in free-range flocks, hens may be allowed to develop natural immunity before they start to lay.

There are various medications (coccidiostats) that can be added to the starter and grower feed in very small doses continuously, to help prevent infection.  In fact, some commercial feeds contain a low level of coccidiostat.  It’s best to get advice from a local expert and/or veterinarian to find out if it would be wise to give your chickens medicated feed.

If there is an outbreak in your birds, you can treat them by giving a course of anti-coccidial medication for 10 to 14 days.  Remember to respect the ‘withholding period’ for eggs and meat from treated birds.  This is the period of time that should elapse after treatment before meat or eggs are used for human consumption.

Roundworms and tapeworms

Roundworms are relatively common in free-range hens, and the main signs are diarrhoea and weight loss or a drop in production.  The lifecycle involves worm eggs being passed in faeces to contaminate the environment, and birds become infected when they pick up the eggs when foraging.

There are many types of intestinal worms, including ascarids, the caecal worm, hairworm and gapeworm.  If you want to test for worms, your veterinarian may be able to arrange for laboratory tests on faecal samples.

Control of worms is best achieved by range management to prevent the build-up of worm eggs on the ground.  This means removing accumulated droppings, rotating outdoor paddocks, and liming, ploughing and re-grassing badly contaminated ground.

For treatment, poultry anthelmintics can be added to the feed or water, and in small flocks, birds can be individually dosed with anthelmintics such as ivermectin.  An expert such as a veterinarian can advise on the best option for your flock.  With anthelmintic treatment, be mindful of the withholding times (the time that should elapse before eggs or meat are eaten).

External parasites (ectoparasites)

External parasites are those that live on the skin, and the most common types are mites and lice.  They can occur in birds in any management system and tend to be more severe in birds in poor body conditions.  But external parasites can cause ill-thrift too, so as with internal worms, once birds are infested, it tends to be a downward spiral.

Dust bathing seems to help control infections, so in many free-range systems, lice and mites don’t usually cause problems.

Mites: Mites like the northern fowl mite, the red mite and the scaly leg mite are tiny and are not easy to see with the naked eye.  They cause itchiness in birds and sometimes in handlers too.  Red mites live in cracks in the perches and houses during the day and feed from the birds at night, so dust-bathing during the day will not help get rid of them. They are blood-sucking and even moderate infestations can cause a drop in egg production and anaemia.

Scaly leg mite causes painful thickening and distortion of the legs.  This can be treated by spraying the legs with fly spray or using a mix of one part kerosene to two parts linseed oil and dipping the legs quickly to the hocks or painting it on every few days until the condition clears up, or in warm water then oil with a petroleum base. You can also treat perches with kerosene.

To get rid of red mites and scaly leg mites in the environment, perches and wooden surrounds can be coated with creosote.  This is an old-fashioned remedy that can still be effective.   Fly spray can be used to spray small areas.  Treatments should be repeated 4 weeks later.

Northern fowl mites live on the birds all the time so they are harder to eradicate.  There are various chemical treatments that can be dusted on, and it is best to discuss the available options with an expert.

Lice: To check for lice, pick the bird up, tip it upside down and open the feathers around the vent area.  Lice are quite easily spotted and the eggs (nits) are usually clearly visible.  Lice cause itchiness by feeding on feathers and skin, and affected birds scratch themselves and may lose feathers.  There are various treatment options, and poultry dusting powders for lice are usually readily available.  Dog and cat flea powders can also be used.  Treatments should be repeated in two to three weeks to get rid of lice that have hatched since the last treatment, and regular checks should be made after that.

Remember that it is easiest to treat birds at night because they are quieter and more easily handled.

Quarantine new birds

If you are bringing new birds into your flock, it’s wise to isolate them from your resident birds until you have made sure they don’t have internal or external parasites.  This might mean treating them before releasing them onto your farm.