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DEFICIENCY DISORDERS

Deficiencies of selenium and vitamin E cause numerous disorders, which can take very variedclinical forms and involve different organs and systems. The majority of these disorders have theirorigin in the oxidative damage caused by free radicals, while localisation and characteristicsdepend on the species affected, the type of diet and managerial factors.

1. Disorders responsive to Vitamin Ea. Encephalomalacia in chicks (Crazy chick disease)b. Erythrocyte haemolysis in chicksc. Steatitis - adipose tissue of chicksd. Testicular degeneration and sterility in rabbits and chicks.e. Nutritional muscular dystrophy in chicks and rabbits - skeletal muscles

2. Disorders resulting from the combined deficiencies of selenium and Vitamin Ea. Hepatic liver necrosisb. Exudative diathesis in poultry

c. Infertility in ewes and cowsd. Nutritional muscular dystrophy:i. WMD in lambs, calves and kids - skeletal and heart muscles

ii. In the gizzard and heart of the turkeyiii. In the skeletal muscle of chickens

3. Disorders responsive to selenium alonea. Fibrotic degeneration of chick pancreas

POULTRY

Exudative diathesisExudative diathesis is a pathology characterised by severe edema, predominantly localised in thebreast, wings and neck. It derives from excessive capillary permeability following the oxidativedamage due to a deficiency of selenium and vitamin E. It occurs in chickens between 2 and 6weeks of age with edema, loss of weight, weakness of limbs, a bluish coloration of the skin and anincrease in mortality. Broilers are often severely penalised for the yellowish coloration of the flatinside part of the legs, due to transudation of plasma into subcutaneous tissue.

Encephalomalacia (Crazy chick disease)Encephalomalacia affects chickens of 2-6 weeks, fed on diets deficient in vitamin E and possiblyrich in polyunsaturated fatty acids. It is a consequence of oxidative damage to encephalicstructures, with an increase in the fragility of capillaries. In chickens, the brain is easily affected bya deficiency of vitamin E, due to the low vitamin content, the high presence of polyunsaturated fattyacids and the low activity of antioxidant enzymatic systems. Encephalomalacia occurs withnervous symptoms and prostration, while at the necroscopic examination, haemorrhagicencephalic lesions are found. Selenium is unable to prevent this pathology, while syntheticantioxidants are only partly efficacious.

Nutritional muscular dystrophyMuscular dystrophy is a degenerative disorder of skeletal muscle, a consequence of the formationof microthrombi in the arterioles and capillaries. It is characterised by the degeneration of musclefibre, particularly of the breast, but also occasionally of the thigh. In the chicken, it is often foundwith exudative diathesis and it tends to occur only when the diet is poor in both vitamin E and

sulphur amino acids (methionine and cysteine). Unlike the situation in chickens, in the turkey thedisorder predominantly affects cardiac muscle and the gizzard and is not correlated to aconcomitant deficiency of sulphur amino acids.

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RUMINANTS

The typical deficiency form in ruminants is White Muscle Disease. It usually affects young animalsand assumes an endemic character in zones with pastures poor in selenium. This degenerativeform can affect both skeletal muscle, giving rise to symptoms of motor difficulty and the heart,causing the sudden death of animals. Calves and lambs can be stillborn or die during the first fewdays of life, while borderline deficiencies can cause pulmonary edema and increase the incidenceof respiratory pathologies.In addition to preventing White Muscle Disease, it is widely recognised that selenium and vitamin Eare important in ensuring animal health and in preventing numerous disorders which can severelycompromise the profitability of rearing establishments. In cattle and ovines-caprines, theseantioxidant substances are able to reduce many reproductive disorders, such as retained placenta,metritis and cystic ovarian disease, increase resistance to infections, improve udder health andincrease productive indices.