Trace minerals are essential to an animal for normal health and productivity. They act as the keys that assist in the utilisation of energy and protein within the body. As such they are important for normal growth, meat, wool and milk production, fertility and immunity. Trace minerals are required constantly but at certain times such during the growth of a young animal or during pregnancy and lactation or when experiencing increased stress for whatever reason, the animal’s demand can increase.
Deficiencies can present either as overt clinical disease or, more commonly, subclinically with less obvious signs but still significant productivity losses. If clinical disease is present this often the “tip of the iceberg” and many more animals are deficient and not showing obvious signs.
Deficiencies of selenium cobalt and copper are common in ruminants in many parts of Australia. We will cover selenium deficiency in the next section.
Importance of selenium
Selenium has a number of important functions. It acts as an antioxidant to protect tissues from cell damage as is also involved in normal healthy metabolism and function of the immune system.
Many areas of Australia are predisposed to selenium deficiency such as regions with lighter soil types, acidic basalt or granite or sandy soils, higher rainfall regions (450 – 500mm per year), clover dominant pastures and areas of heavy or long term fertiliser application e.g. high superphosphate application.
Pasture selenium content is also diluted during periods of rapid pasture growth therefore there can be a seasonal pattern to deficiency. Furthermore, selenium levels are dependent on pasture species and shallower rooting species (white clover or perennial ryegrass) may have lower levels than deeper rooted species (lucerne)
Periods such as weaning, pregnancy or lactation will increase the demand for selenium and sometimes tip animals which might be marginally deficient over into clinical disease