Chicken Health and Parasite Prevention


This article is written by Pet Circle veterinarians, Dr Nicole Wynne BSc BVMS MANZCVS (Unusual Pets) and Dr Emilee Lay BVSc BSc (Vet) Hons

Prevention is better than cure, and that’s certainly the truth for keeping backyard chickens in good health. Chickens are prone to many communicable diseases, and some prior planning can reduce the risk of your chickens getting sick. 

As chickens are food-producing animals, it is important to ensure that any medication they receive, whether as treatment or prevention, is on-label for food-producing animals, and you adhere to any recommended withholding period for eggs.

A withholding period is a period of time after being given a medication where any products from that animal cannot be used for human consumption. This period starts from when the last dose of medication was given. For example, for a 7 day withholding period, the last dose of medication given on Monday morning means that eggs are not suitable for human consumption until the following Monday. These products should not be fed back to chickens either, as they may contain drug residues.


While vaccinated chickens are certainly at a much lower risk for disease than non-vaccinated chickens, it can be difficult obtaining the vaccines as they are formulated and designed for production systems. This means that vaccines often have to be given soon after hatching, or into the egg, for maximal efficacy, and may not be very useful if given to an older chicken. These vaccines also come in vials that contain thousands of doses with a short use-by date, which works fine for farms that expect to vaccinate thousands of chickens in a day, but not for smaller backyard flocks or pet chickens. 

The best way at this stage to get vaccinated chickens is to source your chickens from a larger hatchery where they come fully vaccinated. Diseases that are important to vaccinate against include Marek’s disease, Newcastle disease, infectious laryngotracheitis, and infectious bursal disease.


Ensuring that new additions to your flock don’t bring in communicable diseases is one of the most important things you can do to keep your chickens healthy. To practice good biosecurity, you will need to set up a quarantine area that is as far away as possible from your flock’s living area. This area should have its own food, feed and water containers, bedding, tools, and footwear. The main idea is to reduce cross-contamination between the old chickens and the new chickens. 

New chickens should be kept in quarantine for at least 2 weeks before introducing them to the existing flock. During this time, they can also receive parasite treatments for internal and external parasites.


Keeping chickens clean can certainly be a difficult task, especially when they live on natural surfaces like soil, straw, or shavings. However, there are some tips and tricks that can make cleaning up a lot easier and more effective. 

Having a movable coop allows you to rest the ground, reducing the risk of external parasite infestation like fleas and lice. Dividing your backyard into sections, and rotating your chickens through those sections also helps to reduce the risk of intestinal parasites, and keeps your soil and grass safe from excess manure. 

Hemp bedding is an excellent, easily maintained bedding material that not only is super absorbent, but also easy to spot clean. Soiled portions of bedding should be removed daily, and a full clean out should be done fortnightly at least. Hemp bedding is also fully compostable, and makes excellent compost when soiled. 

Parasite Prevention

As mentioned before, while parasite prevention is important for keeping your flock healthy, all medications must be on-label for food producing animals. Vetsense Kilverm Poultry Wormer is an easy to use in-water wormer that is on-label for chickens with a zero day withholding period for eggs. Chickens should be wormed every 4 months. Alternatively, a vet can perform a faecal egg test every 4-6 months. 

Chickens are also prone to suffering from external parasites, including stickfast fleas, lice, and mites. External parasites can be very difficult to eradicate, as some parasites like fleas have a lifestage in the environment. Inca Pestene Insect Powder is an excellent treatment and preventative for external parasites, and can be used on the birds, as well as in the environment. The powder can be sprinkled into the bedding, or in their dust baths. This can be used as often as weekly. There is no withholding period for eggs. 

External parasites include lice, fleas and stickfast fleas, and mites (like scaly leg mite). Lice are easy to see with the naked eye, and their eggs can be seen coating the feather shafts. Mites can be difficult to see, and the largest mites are no larger than a pinhead. However, the effects of the mites can be easy to see, with scaly leg mites causing thickened, crusty legs. Stickfast fleas live up to their name, and they are usually seen as black specks on unfeathered areas like the legs, face, and comb.

Common Illnesses

Regardless of the illness, it is important that your chicken sees a veterinarian for any health issues. Your veterinarian will be able to recommend a more effective course of treatment, as well as advise you on potential withholding periods for that treatment. Although chickens are hardy animals, they often hide symptoms of illness, and once they become overtly unwell, it is likely that they are already very sick. 


Chickens are very prone to respiratory diseases, but it may not be immediately apparent. Respiratory illnesses can show us as lethargy, weight loss, or abnormal egg production in the beginning, before progressing to difficulty breathing, nasal and oral discharge, loss of appetite, and potentially death. Other symptoms may include a change in their vocalizations, hiding away, a change in normal flock hierarchy, and multiple chickens being affected.

It is important to be careful when handling chickens that may have a respiratory disease to be mindful of hygiene, hand-washing, and to avoid touching your face. Some respiratory diseases in chickens can be zoonotic, which means that they can be passed to humans. 


Diarrhoea is a common symptom in chickens, and there can be several causes. Intestinal worms and parasites can cause diarrhoea, as well as anaemia, respiratory difficulties, weight loss, and death. Other causes of diarrhoea include bacterial, fungal, or protozoal infections, inappropriate feeding, viral infections, and heat stress. 

Symptoms of diarrhoea include a change from the usual formed droppings to droppings with a watery consistency, malodorous smell, blood, and bright green colouration. Chickens may have faecal and urate staining along the feathers surrounding their vents. Other less specific symptoms of diarrhoea include lethargy, inappetance, faecal staining on eggshells, and even sudden death. 

There are also conditions that can mimic diarrhoea, but may not be gastrointestinal in origin. Coelomic effusions (buildup of fluid in the body cavity) may initially look like watery droppings. This is one of the reasons why a vet visit is essential to figure out the true cause.

Heavy metal poisoning is another common gastrointestinal disease that is more likely if you are living in an older house or property, dating from before regulations stopped the common use of lead in household products, hardware, and paint. While heavy metal poisoning can also cause neurological symptoms, diarrhoea is also a common symptom, and may be the first symptom that develops.

Crop abnormalities

The crop is an outpouching of the oesophagus that stores food before it passes into the stomach. In chickens that have recently eaten, you can normally feel it as a soft, moldable lump midway down the neck. While the crop is a simple organ, it can still run into trouble. 

Common issues with crops include impaction and infection. Impaction occurs when the food item (or not food item!) they’ve ingested is unable to pass into the stomach. Long grass is the most common cause for impaction, and can occur when chickens are let out into long grass, or during spring and autumn when grass grows rapidly. Chickens do best with grass no higher than 10 cm. 

Crop infections can be bacterial, fungal, or protozoal, and so it is important to visit a vet before giving any medication, as an antibiotic will not work for a fungal or protozoal infection, and an anti-fungal won’t work for a bacterial or protozoal infection! 

Symptoms of crop disease include regurgitation, bad breath, nasal discharge, a large, visible lump on the neck, inappetance, and lethargy.

Reproductive disease

Sadly, many egg-laying breeds of chickens are prone to developing reproductive disease due to being bred for higher egg production. ISA Browns, a common backyard and production breed, almost always develop reproductive problems after the age of 2. 

Hens suffering from reproductive disease may not always produce abnormal eggs, but the presence of abnormal eggs is always a cause for concern. Abnormal eggs include shell-less eggs, soft-shelled eggs or wrinkly eggs, lash eggs (not an egg, but an abnormal accumulation of material within the reproductive tract), and oddly shaped eggs.

Other symptoms of reproductive disease include diarrhoea or other abnormal stools, heavy breathing, an abnormal posture or gait, and a swollen abdomen.

Another type of reproductive disease is egg-binding. This isn’t as common as people think, as many breeds of chickens are bred to produce eggs, and so tend not to have issues with egg binding unless their diets or environments are inappropriate. Unfortunately, many chicken owners misdiagnose their chickens with egg-binding when they are suffering from something else, and by the time their home treatments haven’t worked, it can be too late. 

Musculoskeletal issues

Most chicken owners know about bumblefoot (pododermatitis). Risk factors for chickens developing bumblefoot include rough or abrasive flooring, hard flooring, unhygienic surroundings, obesity, or lameness. However, chickens can suffer from other muscular and skeletal problems too. Paralysis is a common issue that can be caused by Marek’s disease, and affected chickens display a characteristic splayed posture, with one leg in front and the other behind. 

Chickens can also get gout, which is caused by a painful buildup of uric acid crystals in joint spaces and in organs. Gout in birds is caused by dysfunctional kidneys, and produces symptoms such as hot, swollen, painful joints, lameness, deformed toes, reduced range of motion, and knobbly joints. This requires veterinary attention for investigation of the kidney dysfunction, as well as pain relief and reduction of the uric acid buildup.

Chickens can also get osteoarthritis, just like cats, dogs, and humans! Osteoarthritis normally affects longer lived breeds such as Silkies. Symptoms of osteoarthritis may be difficult to see, as they include behaviours that may also just be due to an older chicken slowing down. Symptoms include lameness, getting around more slowly, sitting or standing in unusual postures, sensitivity to touch, and reduced appetite. To fully diagnose the extent of osteoarthritis, your vet may put your chicken on a pain relief trial, or recommend x-rays.

Further Reading

Want to read more? Check out our other articles:

Feeding Chickens

How to Start Keeping Chickens

Understanding Chicken Behaviour

Backyard Chicken Guide

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