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    Fatty Liver Hemorrhagic Syndrome In Chickens

    A white hen eats kale from a human's hands while other hens stand in the background
    Diet seems to play a crucial role in the development of fatty liver hemorrhagic syndrome. Photo: Jo-Anne McArthur / #unboundproject / We Animals Media

    This resource has been updated as part of the veterinary review process. It was originally published on July 25, 2018.

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    Veterinary Review Initiative
    This resource has been reviewed for accuracy and clarity by a qualified Doctor of Veterinary Medicine as of January 2023.

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    What Is Fatty Liver Hemorrhagic Syndrome?

    Fatty Liver Hemorrhagic Syndrome (FLHS) is a non-infectious disease of chickens that typically presents as sudden, unexpected death in hens who are overweight (“over conditioned”). First reported in commercial egg-laying hens in 1956, this disease continues to be a major cause of death in commercial operations. However, this is not a disease that only occurs in commercial settings – FLHS is also one of the most common non-infectious causes of death in backyard chickens. 

    The exact cause of FLHS is not fully understood but is believed to be a combination of nutritional, genetic, environmental, and hormonal factors. These include the following:

    • Excessive consumption of high-energy diets plus restricted exercise
    • Being overweight
    • Exposure to high temperatures 
    • Egg-laying/increased estrogen production 
    • A genetic predisposition to the disease

    Death from FLHS is caused by liver rupture and massive hemorrhage. Based on necropsy findings, it appears that some individuals who die from massive hemorrhage also had previous, smaller hemorrhages from the liver.

    Who Is Most Often Affected?

    FLHS is typically associated with high-energy diets and restricted exercise and is most often seen in actively laying females in the spring and summer. A retrospective case study that analyzed 76 reported cases of FLHS in backyard chickens (diagnosed at necropsy) found that:

    • The majority (74) of the chickens were female
    • The majority (69.7%) were actively laying
    • The majority (97.4%) were classified as overweight to obese

    Based on these findings, the authors suggest that obesity alone can lead to FLHS. While the findings of this study certainly support the notion that FLHS primarily affects females, the authors state, “The development of spontaneous FLHS in roosters cannot be evaluated due to the very low number of birds.” These low numbers are likely due to the fact that most backyard flocks consist primarily of hens.

    What Are The Signs Of FLHS?

    Unfortunately, this disease often causes unexpected death without an individual first showing obvious signs of clinical disease and can only be diagnosed with a necropsy exam. However, characteristics and signs seen in birds who have died from FLHS include sudden death in actively laying hens, obesity, and chickens fed a high-energy diet with limited exercise. The disease may often occur during warm, summer months. Chickens may show non-specific signs of disease such as lethargy, pale comb, dandruff on wattles, refusal to eat, and puffed up feathers. A sudden, unexplained drop in egg laying and brittle eggshells have also been associated with this disease.

    Always Seek Veterinary Guidance For Sick Chickens
    Anytime a resident is showing signs of illness, be sure to contact your veterinarian for guidance. As prey animals, chickens mask signs of illness until they are no longer able to do so. By the time clinical signs are apparent, the underlying cause may have been progressing for some time. To learn more about what to look for when observing your chicken residents, check out our resource here. 

    How Can The Incidence of FLHS Be Reduced?

    If there have been cases of FLHS at your sanctuary, be sure to talk with your veterinarian about possible ways to reduce the likelihood of additional cases. According to Merck Veterinary Manual, most attempts to prevent or treat FLHS experimentally have involved diet modification. Below are dietary changes that may reduce the incidence of FLHS. However, we always recommend working with an experienced veterinarian and/or avian nutritionist when determining the most appropriate diet for your residents and when considering modifications to their standard diet.

    The incidence of FLHS may be reduced by diet modifications such as:

    • Switching to a lower energy food (as the total energy in the diet increases, the risk of FLHS also increases, so offering a lower energy food may help reduce the risk)
    • Continuing to provide the same energy content but replacing carbohydrates with supplemental fat
    • Incorporating alfalfa meal, wheat bran, or dried brewer’s yeast into your residents’ diet
    • Providing diets that contain proper amounts of selenium and/or vitamin E
    • Avoiding chelated trace minerals

    Because the exact cause of FLHS is not fully understood, it can be challenging to know exactly what preventative measures sanctuaries should take to protect their residents. However, some care practices that you already have in place to promote resident health may go a long way in also reducing the likelihood of FLHS. For example, providing your residents with a balanced diet, as recommended by your veterinarian, that takes into consideration the needs of the individual based on their age, sex, breed, and laying status can help maintain residents at a healthy weight. Tracking your residents’ weight and body condition during routine health checks can help catch unhealthy weight gain early, allowing you to take necessary action to get them to a healthier weight. Even the living spaces you provide may have an impact, as restricted exercise may contribute; thus, providing spaces with plenty of room for activity and exploration may be beneficial. Protecting residents from the heat is an important part of sanctuary care regardless of its effect on the incidence of FLHS, but given the fact that warm temperatures appear to play a role in the development of FLHS, providing living spaces that include shaded areas, cool water footbaths, cooling systems, etc. (in conjunction with offering a healthy diet) may also help reduce the incidence of FLHS.

    For more information about FLHS and ways to protect your residents, we recommend having a discussion with your veterinarian.


    Overview of Fatty Liver Hemorrhagic Syndrome in Poultry | The Merck Veterinary Manual

    Current Therapy In Avian Medicine And Surgery, First Edition | Brian L. Speer, DVM, DABVP (Avian Practice), DECZM (Avian)

    Fatty Liver Hemorrhagic Syndrome in the Backyard Chicken: A Retrospective Histopathologic Case Series

    Fatty Liver Haemorrhagic Syndrome | Diseases Of Poultry (Non-Compassionate Source)

    Fatty Liver-Hemorrhagic Syndrome Observed In Commercial Layers Fed Diets Containing Chelated Minerals (Non-Compassionate Source)

    Fatty Liver Hemorrhagic Syndrome | The Poultry Site (Non-Compassionate Source)

    Non-Compassionate Source?
    If a source includes the (Non-Compassionate Source) tag, it means that we do not endorse that particular source’s views about animals, even if some of their insights are valuable from a care perspective. See a more detailed explanation here.

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