Important trace elements or ‘micronutrients’ required by pasture-based dairy cattle include the minerals copper (Cu), selenium (Se), cobalt (Co), iodine (I) and zinc (Zn).
They are needed for the function and metabolism of many enzymes as well as some vitamins.
Deficiencies occur due to insufficient levels of the actual trace element in the diet (‘primary’ deficiencies) or when the pasture contains something else that reduces the uptake of the trace element (‘secondary’ deficiencies).
Copper
Copper is required for the development of bone and connective tissue, growth, skin and hair pigmentation, immune function and reproduction.
Although primary deficiencies are not common, secondary deficiencies due to a high intake of molybdenum, sulphur and iron often occurs in pasture-based diets, especially in winter and spring.
Clinical signs of copper deficiency include ill-thrift, poor hair coat, anaemia, suppressed immune system, bone abnormalities and diarrhoea.
A veterinary diagnosis is required through blood and liver samples along with a thorough investigation of other contributing factors.
Selenium
Selenium is required for normal growth, fertility, disease resistance, passing of foetal membranes after calving, milk production, calf viability and immunity.
Primary deficiencies can arise in areas with sandy or volcanic soils with high-risk regions being those with higher winter rainfall or areas with more than 500mm annual rainfall.
Clinical signs of selenium deficiency include white muscle disease in calves (sudden collapse, weakness, diarrhoea), ill-thrift, anaemia, poor milk production, poor fertility, retained foetal membranes, abortion and stillbirth.
A veterinary diagnosis is required through blood and liver samples.
Cobalt
Cobalt is required for production of vitamin B12 and B1, energy metabolism in the rumen, fibre digestion and immunity. Deficiencies are most common in regions with volcanic soils or those rich in igneous rocks.
Clinical signs of cobalt deficiency are related to lack of vitamin B12. These include ill-thrift, poor appetite, diarrhoea, suppressed immune system, anaemia, neurological abnormalities and death.
A veterinary diagnosis is required through blood and liver samples.
Iodine
Required for thyroid hormone function, iodine is needed for energy metabolism, milk production, growth and reproduction.
Primary deficiencies occur in regions where soil concentrations are low and secondary deficiencies occur in cattle grazing forages that contain substances that inhibit uptake, for example brassicas, sorghums and white clover.
Clinical signs of iodine deficiency include poor growth, reduced milk yield, infertility, abortion, stillbirths and retained foetal membranes.
A definitive diagnosis is difficult and veterinary advice should be sought for further advice.
Zinc
Zinc is required for growth and production, reproduction, skin, hoof and hair strength, and immune function.
Primary and secondary deficiencies can occur and the need for zinc supplementation will vary from farm to farm. Excess dietary copper and iodine can interfere with dietary absorption of zinc.
Clinical signs of zinc deficiency include deterioration of hair, skin and hooves, poor growth and infertility.
A veterinary diagnosis is required through sampling of available feed, blood and liver samples.
Treatment and prevention
Trace element deficiencies can be treated and prevented using a variety of options.
It is important to obtain a veterinary diagnosis of trace element deficiency prior to any supplementation as toxicity of some trace elements can occur where supplementation is not necessary.
Options for supplementation include top dressing of pasture, oral mineralised drenches, pour-on products, injectable products, in-feed supplementation and sustained release intra-ruminal pellets.
If you are concerned about trace element deficiency in your herd, please discuss diagnosis, treatment and prevention options with your veterinarian.
Reference: Diseases of cattle in Australasia / edited by T.J. Parkinson, J.J. Vermunt, J. Malmo, R. Laven. Massey University Press, Auckland, New Zealand, 2019.
Dr Gemma Chuck works for Apiam Animal Health in the dairy operations team where she writes technical service programs for farmers and vets.