Hepatosis Dietetica (HD)
Age affected: Weaners, growers / finishers.
Causes: Vitamin E or selenium deficiency.
Effects: Sudden death, vomiting, staggering.
Hepatosis dietectica results from a deficiency of selenium and or vitamin E (alphatocopherol) in the ration and is exacerbated by low methionine and cystine levels and high fat levels in the diet. Oxidised fat, copper and the wet storage of cereals may all reduce the Vitamin E levels. The presence of low levels of selenium in grain grown on selenium deficient soils may exacerbate the condition, as may soya and selenium-retaining bran from wheat offals and high fat content. Alpha-tocopherol acts both as an antioxidant and as a stabiliser of membrane lipids. A specific loss of membrane-bound arachidonic and linolenic acids occurs in Vitamin E deficiency and this is associated with low dietary levels of these acids. Selenium forms part of glutathione peroxidase, an enzyme which acts on oxidised polyunsaturated fatty acid radicals. Selenium therefore has a sparing effect on Vitamin E, the action of which in turn is related to methionine and cystine levels. The major clinical signs of this complex deficiency appear to result from the effects on energy metabolism. The cells most severely affected in the pig are hepatocytes (liver cells) and muscle cells in the heart and skeletal muscles.
Mode of transmission
This condition is not transmissible, but may arise in successive groups of pigs consuming the same diets.
Sudden death is most commonly seen. It occurs in young growing pigs usually 3-4 months of age. Affected pigs may be depressed, vomit or stagger but are usually found dead. Deaths may occur after handling and affected animals within a group may show some signs of circulatory embarrassment such as lethargy, cyanosis and dejection. Muscle tremor may occur, especially at the shoulders. There may be stiffness, a limp or recumbency. Members of an affected group may have a poor growth rate. Selenium levels in plasma are related to plasma glutathione peroxidase (GSH Px) activity and low levels of this enzyme are found in selenium deficiency. Serum levels of less than 0.025 g/ml and liver levels of less than 0.10 mg/kg are present when selenium deficiency is the major factor.
Depression, vomiting, staggering and sudden death in a group of 3-4 months old pigs might suggest hepatosis dietectica, but the post-mortem findings are more likely to suggest it. Confirmation depends on the demonstration of low dietary levels of alpha-tocopherol. 10,000 IU (60 g) per tonne is considered adequate in sow feed and a minimum of 1,500 IU (5 g) per tonne in rations for pigs up to 90 kg. Histories of storage of grain in propionic acid, etc are suggestive. Levels of plasma alpha-tocopherol are less than 1 mg/L (normally in excess of 1.9 mg/L). Response to alpha-tocopherol treatment is confirmation although selenium may also have some effect.
Lesions include the presence of excess clear pericardial fluid, pulmonary oedema and enlargement of the heart which is often pale in colour. The liver is pale and mottled or haemorrhagic. In long-standing cases regeneration of liver lobules may be seen on the surface as reddish spots or tags in a yellowish liver. Rupture of the liver may occur, there may be an obvious fissure with an attached blood clot and the abdomen may be filled with blood. Microscopical findings include degeneration of the arterioles, and the presence of microthrombi in the liver.
Treatment and prevention
Injection with tocopherol or tocopherol-selenium preparations is of value in affected groups of animals. Vitamin E is also available as a component of the fat soluble vitamin mixtures. Control depends upon ensuring that adequate levels of dietary Vitamin E are present in the final ration [10,000-20,000 IU (3.0-6.0g) /tonne]. The suggestion that Vitamin E should be included at five times the fat percentage of the ration measured in mg/kg feed is usually adequate, but actively oxidising fats may need up to 20 times the fat percentage. The addition of selenium to such diets to give a final concentration of 0.8-1.1 ppm increases growth rates in weaned pigs and reduced the incidence of hepatosis dietectica. Selenium uptake is most efficient in the organic form (as methionine Se, cysteine Se) but inorganic selenium can also be absorbed. Vitamin E may be restored to normal within a few hours by injection but may take 2 weeks by feed supplementation.