Improving trace element nutrition of grazing animals, in a way that is cost
effective and that meets consumer perceptions and preferences, is a continuing
challenge. This review focuses on research over the past 10 years, addressing
issues and perspectives on the roles, risks of inadequacy, and supplementary
remedies of key trace elements, both essential and deleterious, which have an
impact on the productivity and product quality of grazing livestock throughout
Australia and New Zealand. The emphasis is on copper (Cu), cobalt (Co), iodine
(I), selenium (Se), and, to a lesser extent, zinc (Zn) — the trace
elements most frequently found to be deficient in parts of Australia and New
Zealand. Research continues to elucidate new roles for trace elements in the
animal, and as this leads to a better understanding of requirements,
diagnostic criteria and supplementation strategies need re-evaluation. Newer
perspectives on marginal deficiency for Cu, I, Se, and Zn are given and issues
for risk management discussed. Advances in sustained delivery of trace
elements such as Co (as vitamin B12), I, and Se are
reported. The diagnosis and management of marginal Cu deficiency continue to
be difficult, especially in New Zealand where recent work has shown that
dietary antagonists [iron (Fe), molybdenum (Mo), and sulfur (S)] may
impair Cu absorption at lower intakes than previously thought. There is still
a dearth of scientific data on the advantages of using so-called organic trace
element supplements (metals complexed or chelated with amino acids or
peptides). Nevertheless their usage continues to increase. There is increasing
evidence that trace elements influence the pathophysiology arising from the
ingestion of toxins. This review summarises recent work on the role of Co in
annual ryegrass toxicity; Cu, Se, and Zn in lupinosis; Cu and alkaloid
toxicity; Zn and facial eczema; and Co and white liver disease. Trace elements
are required to support immune function (e.g. as imposed parasite infection)
and marginal deficiencies may be exacerbated by an immunological challenge.
The roles of Cu, Co, Mo, Se, and, to a lesser extent, chromium and Zn have
attracted attention and under conditions of stress there may be an additional
need for these elements. Diversification in farming has led to the
introduction of species such as deer (Cervus), alpacas
(Camilids), emus, and ostriches
(Ratites) and the paucity of information on trace
element requirements for these species, and also for horses, indicates the
need for further work. The effect of supplementation on trace element
composition of meat, milk, and wool is also reviewed, both in terms of product
characteristics and human health. Of the deleterious elements, cadmium has
attracted the most interest and concern because of its introduction into the
pastoral system from phosphate-based fertilisers.
