Background and history

MHD (also called a myopathy) is a specific disease of heart muscle and a common cause of sudden death. It is one of several diseases associated with a lack of vitamin E.

During the past few years problems associated with either the lack of availability of vitamin E and selenium, or absolute deficiencies have become major problems on some farms. These have arisen with the practice of using polyunsaturated fats in diets as sources of energy. The actual principles of vitamin E are called tocopherols and they are widespread in feed stuffs including vegetable oils, cereals and green plants.

Tocopherols are used in pig rations as dl-alpha-tocopherol acetate and measured in international units. For the international unit (iu), 1iu of vitamin E is defined as 1mg of a standard preparation of a specific tocopherol acetate.

The recommended requirements to give a maximum boost to the immune system range from 75–220iu/kg, according to age of the pig and diet: in the first stage creep 220, the second stage 150, the grower 100, the finisher 60 and sow 50 iu/kg. These levels are probably higher than those necessary for maximum growth, which may be 50 percent less.

The function of vitamin E in the pig

Vitamin E helps to maintain the integral structure of muscles in the digestive and reproductive systems and is involved in the synthesis of certain amino acids and vitamin C. It has a close relationship with selenium metabolism. The less selenium in the diet the greater is the requirement for vitamin E.

• To prevent the breakdown of oxygen at a cellular level (oxidation) when toxic products including hydrogen peroxide and hydroxyl radicals are produced. These oxidising agents are powerful tissue poisons.
• It acts as a tissue antioxidant. Heart muscle is particularly sensitive to oxidising agents, the reason why MHD is so common.
• To increase the efficiency of the immune system. Adequate levels must be available at critical times particularly as maternal antibody is dropping and pigs are being challenged by infectious agents. This highlights the importance of both diet quality and levels of energy lysine and vitamin E at these times.
• It helps to maintain the integral structure of muscles in the digestive and reproductive systems.
• It is involved in the synthesis of certain amino acids and vitamin C.
• It has a close relationship with selenium metabolism.
• Selenium is an essential nutrient in its own right and part of an enzyme called glutathione peroxidase which also acts as an antioxidant and thus has a complementary role to vitamin E.
• Polyunsaturated fatty acids (PUFAs) cause considerable oxidation at tissue levels and when added to diets 3iu of vitamin E should be added for each gram of PUFA.

Related diseases include:

• Gastric ulcers – These are often stress oriented and the incidence increases where vitamin E levels are low.
• Hepatosis dietetica (HD) – A condition where there is necrosis or death of liver cells.
• Muscular or nutritional dystrophy (MD) (also called a myopathy) – This results from a degeneration of muscle fibres whether they be skeletal smooth or cardiac. Oedema or fluid is often produced around the tissues and muscles (PSE) as a result.
• Reproduction disorders – Vitamin E is involved in sperm production and ovarian function. The actual role of vitamin E on the farm is difficult to clarify.
• Actinobacillus pleuropneumonia.
• Glässers disease.
• Streptococcal septicaemias.
• Post-weaning respiratory syndrome.
• Porcine reproductive and respiratory syndrome (PRRS).
• Swine dysentery.
• Those diseases that occur during periods of immunosuppression.

Clinical signs

Piglets

Become sensitive to iron injections if sows deficient.

Weaners and growers

MHD is usually associated with sudden deaths in rapid growing pigs without any prior clinical signs. Usually the best pigs in the pen are affected and they range from 15–30kg in weight. Diets being fed often contain high levels of fats and yet in many cases vitamin E levels appear within normal ranges.

Clinical signs vary according to the system affected and include:

• Sudden death in rapid growing pigs without any prior clinical signs.
• Possibly increased levels of concurrent diseases if selenium levels are low.
• Pale pigs.

In post-mortem:

• Large amounts of fluid around the heart and lungs.
• Haemorrhagic and pale areas in heart muscle.
• Fluid in the abdomen with pieces of fibrin.
• Pale muscle areas (necrosis) particularly in the lumber muscles and hind muscles of the leg which contain excesses amounts of fluid.
• If the liver is involved it is enlarged and mottled with areas of haemorrhage interspersed with pale areas.

Diagnosis

Accurate diagnosis requires histological examinations of the liver, heart or skeletal muscle. Serum samples should be taken from pigs at risk and tested for levels of vitamin E.

Normal levels are variable from pig to pig however they should be more than 1.8mg/litre. The availability of selenium can be assessed by measuring the levels of glutathione peroxidase in the serum. If levels are less than 0.025µg/ml or 0.1mg/kg in liver a deficiency should be suspected and rations checked.

Causes

• Diet, ie, high levels of fat.
• Vitamin A deficiency.
• Vitamin E and selenium deficiency.
• Rapid growth may be a contributing factor.
• High stocking densities may predispose.
• Grains stored with high moisture content in high temperatures and with fungal growth may have low levels of vitamin E.

Prevention

• If problems persist change to another diet with less added fats.
• Check the levels of PUFAs in the diet.
• Check the levels of vitamin E and selenium.
• Check the levels of vitamin A. If more than 10,000iu/kg this may be increasing the requirement for vitamin E.
• Rapid growth may be a contributing factor.
• Reduce stocking densities if pigs are overcrowded.
• Check there are no parasite burdens.
• Grains stored with high moisture content in high temperatures and with fungal growth may have low levels of vitamin E.
• Do not breed from animals that carry the stress gene.

Treatment

• Where a population is at risk inject all the pigs with vitamin E/selenium eg, dystocel, 70iu vitamin E and 1.5mg per 50kg is adequate, but seek veterinary advice.
• If sudden death in piglets following iron injection – inject sows 14 days prior to farrowing with vitamin E/selenium.
• Water soluble preparations are sometimes available as alternatives.
• Multivitamins that include vitamin E and or selenium may be used. Refer to the recommended treatment levels on the bottle label.
• Move individual pigs to hospital pens for treatment.
• Increase vitamin E levels in creep and growing rations by 100–150iu/kg.