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Avian Gastric Yeast (formally called megabacteria)

By John Moverley.

Your birds are probably infected with avian gastric yeast (megabacteria) at low levels which are not causing any problems. It is when something weakens your birds that they become susceptible to an outbreak. Under these conditions, it can be ignored.

Chicks are more vulnerable and may require special management.

Avian gastric yeast live in the digestive tract. Many birds carry it without any apparent harmful effects, but it can make the bird susceptible to other diseases such as trichomoniasis, feather mite infestation, cnemidocoptic mange and chlamydophilosis (Environment Australia).

It can cause ulceration of the bird’s stomach lining. This leads to loss of blood and tissue fluid, predisposes the bird to secondary infection with other organisms and interferes with normal digestion (Melbourne Bird Vet).

Initially, as the ulceration begins, the birds develop diarrhoea and become fluffed and quiet. As the disease progresses, the birds start to lose weight and as the ulcers deepen and start to bleed the birds become anaemic. This means they have trouble maintaining their normal blood pressure and, as a result, their feet become pale and cold to the touch. In severe outbreaks, 50% or more of the birds can die (Melbourne Bird Vet

The death rate due to an outbreak of avian gastric yeast disease can be as low as 10 percent, or as high as 80 percent. But it depends on the degree of infection, the bird species and the strain infecting the bird (Melbourne Bird Vet).



Avian gastric yeast disease is caused by direct contact with infected food or the droppings of an infected bird. Chicks can be infected when their parents feed them. An animal can also be infected if the yeast microbes are found in the environment.

Many birds carry avian gastric yeast. Rarely is it the primary cause of disease. It is usually a secondary disease triggered by stress, some other disease or poor management practice (Melbourne Bird Vet.

Newly weaned birds are very susceptible.



Avian gastric yeast causes two disease syndromes - acute and chronic (Birds N Ways).

  1. The acute disease occurs when large numbers of birds in a flock become ill suddenly and die within 12 - 24 hours. The birds appear fluffed and quiet and may regurgitate blood-tinged fluid.

  2. The chronic disease is more common. Progressive weight loss leading to emaciation occurs. Birds appear lethargic and try to eat, but don't ingest food. Some display difficulty swallowing and repeatedly stretch their necks and gape. Regurgitation of a clear to white slime coats the head, causing the feathers to be matted. Blood may be present in the regurgitated material. Scant watery droppings or diarrhoea may be present, often with undigested seeds.

Birds infected with avian gastric yeast have the following signs and symptoms:

  • birds continually feeding,

  • diarrhoea,

  • birds become fluffed and quiet,

  • continuous loss of weight,

  • regurgitation of food,

  • excessive food intake followed by loss of appetite and

  • undigested feed in the droppings



If you have very sick and dying birds, it is best to get help and prescribed medication from a vet and be prepared to use a crop needle for administrating the prescribed drug. Treatment usually involves drugs for the yeast and also antibiotics for secondary bacterial infections.

Drinking water treatment often lasts a month and may also need to be repeated after several days.

Thoroughly clean your cage or aviary, if only a small number of birds are unwell separate them and treat separately. If many birds are unwell treat in the aviary after cleaning and keep it clean.

Investigate and correct any problems that could be the trigger for the avian gastric yeast outbreak.


Prevention & Home Remedies:

Avian gastric yeast and many other gut parasites do not grow well in an acidic environment, healthy birds have a naturally acidic digestive tract. So the first step to reducing problems caused by avian gastric yeast is to maintain the birds in a good healthy condition.

If your birds are diagnosed as having avian gastric yeast but are not showing any ill effects, all you need to is to keep maintaining your birds in a good well-managed environment. Under such conditions, this can lead to your birds having a higher immunity to any problems caused by avian gastric yeast infections (Melbourne Bird Vet

Sick birds may stop producing the acids that help them control avian gastric yeast. Prevention and home remedies are based on stimulating the acid gut environment. This is usually done by giving the birds citric acid (a white crystalline powder) at a dose of 1 teaspoon (3 g) to 4.5 – 6 litres or apple cider vinegar (acetic acid) 5 – 10 ml to 1 litre. Being natural nutrients, at the above doses, there is no risk of a toxic reaction, so they can be used fairly freely. Their use also helps ensure that droppings passed build up an acidic dressing in the aviary, helping to inhibit avian gastric yeast survival in the environment (Melbourne Bird Vet


Melbourne Bird Vet

Environment Australia

Birds N Ways

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