Selenium is a trace element, physiologically linked with vitamin E that is essential for optimal growth, fertility and immune function in a wide range of animals. It can also remediate the health impacts associated with excessive intake of minerals such as cobalt and cadmium. Its deficiency in ruminants is caused by a lack or low level of selenium in the soil and pasture. Vitamin E and selenium both have oxidant functions and can partially substitute for one another in the diet. The deficiency plays a role in a wide range of health problems in both cattle and small stock. It is characterized by degeneration (wasting) or breakdown of muscles particularly very young animals hence its other name of white muscle disease.
Conditions influencing selenium deficiency
- Selenium deficient pastures, where animals are fed on locally produced feed without supplementation.
- Areas with sandy soils and high rainfalls are particularly prone to the deficiency disease because of leaching of nutrients from the soils.
- Pasture supplement such as superphosphate can reduce the selenium uptake of plants so that could lead to the deficiency occurring in animals even in areas where selenium levels in the soil are within acceptable range.
- Improperly kept feeds. High levels of unsaturated fatty acids e.g. fish/soya oils, cow’s milk with added vegetable fat causes relative vitamin E deficiency.
- Vitamin E deficient diets and poor quality straw with little concentrate.
- Mineral deficiencies and other environmental stressors such as severe weather events or mustering predispose animals to the effects of selenium deficiency.
- Young animals can show signs of selenium deficiency at birth if the mother did not have adequate supplementation during pregnancy. Young animals are affected at birth or up to 6 months of age but generally between 2 to 16 weeks. The most active ones are affected first.
Signs of the disease
Muscle (musculoskeletal) form
- Lameness. Refusal to move
- Difficulty in walking. Stiff gait
- Skeletal muscles are firm and damaged. The animal shows signs of pain when they are palpated especially on the limbs.
- Have good appetite although they can’t move to eat.
- There is no rise in body temperature
- Some animals may show signs of muscle affection after being driven and become weak.
Heart (cardiac) form
- Sudden death, typically in young ones that are 2-6 months old after or during exercise. New born animals may die soon after birth as a result of damage to the heart that occurs while in the womb. Older animals may also suffer from heart damage.
- Fast heart rate
- Animal breathes fast
- Show general signs of weakness.
- Ill thrift or poor growth particularly in young stock to 18 months old animals.
- Reduced fertility in both males and females.
- Early embryonic deaths (abortions) and still births may rise in incidence as well as post-birth complications such as retained placenta may increase in selenium deficient females.
Abnormalities at slaughter
The thigh muscles are pale with white streaks. Other skeletal (voluntary) muscles such as those in the lumbar region may be affected. Also, the ventricles muscles in the heart may also have these streaks.
How the deficiency is recognized during clinical evaluation
- Muscle damage results in lameness
- Laboratory results indicate marked elevated levels of serum enzymes namely: – creatine kinase (CK) and aspartate aminotransferase (AST).
- Blood levels of a selenium-dependent enzyme glutathione peroxidase are low.
- Liver selenium is below 500nmol/kg or vitamin E below 2.5 µ mol/kg.
Affected animals should be treated with selenium/vitamin E supplements with a method of application of one’s choice.
Note: careshould be taken not to overdose as too much selenium is toxic! Strictly follow manufacturer’s instructions. Selenium should not be supplemented using multiple methods (e.g. with drenches, with vaccines, as feed supplements, as injections or as pasture dressings) at the same time as this could lead to toxicity.
Signs of toxicity include:
- Difficulty in breathing
- Fast heart rate
- Hard pressing
- Collapse followed by death.
It is therefore vital to make sure that when treating for selenium deficiency, one does not give too much of the treatment as it can cause toxicity effect that would be lethal to the animals you are trying to save since the margin between deficiency and toxicity is quite narrow.
- Inject females with selenium and vitamin E one month before breeding also a month before birth and/ or
- Inject offspring at birth and 3-4 weeks of age and possibly again at 12-16 weeks of age (it can be at marking and at weaning).
- Add selenium at 100 ppm to feed.
- Oral drenching with 5 mg sodium selenite during the last week of pregnancy.
- Oral drenching of selenium combined with antihelmintics.