Poultry Health: Hemorrhagic Fatty Liver Syndrome (HFLS)
In past years, several laying hen flocks in Manitoba have had mortality due to Hemorrhagic Fatty Liver Syndrome (HFLS). In a hen with this condition, damage occurs due to the buildup and oxidation of fat in the liver. The hen dies suddenly from internal bleeding when a damaged blood vessel in the liver ruptures. Clotted blood is often found in the body cavity. HFLS should be suspected if many of the dead birds in a flock are overweight and have pale combs. The dead birds should be examined externally to check that the pale combs are not due to injury or prolapse (instead of internal bleeding). Mortality due to HFLS is usually less than 5 percent in flocks with an outbreak of this disease.
To confirm the disease, dead birds must be necropsied by a veterinarian. The necropsy will help to rule out other conditions such as hepatitis splenamegaly that may appear to be similar to HFLS. The veterinarian will also check for cage layer fatigue – a condition sometimes related to HFLS.
In the field, simply finding fat livers in dead hens is not a good indicator of this disease. Laying hens naturally have a high fat content in their livers once they start egg production. Also, the level of fat in the liver of a normal laying hen will vary greatly depending on diet formulation, bird housing density and environmental temperature. If blood clots are not found in the body cavity of some or all of the dead birds, any diagnosis of HFLS should be questioned.
Some researchers who have used amino acid deficiencies and other techniques to artificially induce HFLS have observed a drop in egg production. This production drop may be due to the technique used to create the fatty livers and not directly to the buildup of fat. Experience with commercial flocks indicates that the effect on egg production is often marginal or non-existent.
Body weight control is the key to preventing HFLS. A 1998 survey of five Manitoba flocks with HFLS revealed that the majority of birds dying from this disease weighed 1900 grams or more (see figure). Sixty-five percent of the dead birds with pale combs weighed over 1900 grams compared to 22 percent of the live birds and 12 percent of the birds dying with dark-coloured combs. Eighty percent of the dead birds with pale combs had blood clots in their body cavity. Most of these birds appeared to have been in egg production up to the time that they died. Ninety percent of them had numerous egg follicles and 60 percent had an egg in their oviduct (usually with a hard shell).
Hot weather also appeared to be an aggravating factor in the Manitoba flocks. Improved summer ventilation and mist cooling systems may reduce the mortality. Feed can play a role in causing and treating HFLS. Liver hemorrhaging may be caused by adding chelated iron or high levels of canola meal (over 10 percent) to laying hen rations. Aflatoxin is a feed mycotoxin that can cause fat build up in the liver. Flocks suffering from caged-layer fatigue also appear to be more prone to HFLS, perhaps because the hens over eat as they try to maintain their calcium reserves. High carbohydrate or low fat diets as well as diets deficient in amino acids or essential fatty acids can contribute to fat production in the liver. A common treatment is to feed higher levels of vitamins, such as choline, vitamin B12, vitamin E and selenium, which help to prevent fat accumulation and oxidation in the liver. Adding "fatty liver vitamin packs" to the feed has helped some flocks but not others.
By Carlyle Bennett, M.Sc. (Business Development Specialist – Poultry)
Livestock Knowledge Centre – Manitoba Agriculture, Food and Rural Initiatives
Source: Manitoba Agriculture, Food and Rural Initiatives