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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.
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.
This paper reports on the status of vitamin E and selenium in weaner and adult sheep in Western Australia (WA) during autumn, and its relationship to the incidence of apparent white muscle disease (WMD). A survey was conducted in which blood samples were taken from 10 weaner sheep (8–12 months of age) and 10 adult ewes (3 years of age) from flocks on 38 properties within the main southern agricultural region of WA, an area carrying ~10 million sheep. Deficiency of vitamin E was defined as a plasma α-tocopherol concentration less than 0.7 mg/L. Selenium deficiency was defined as whole blood glutathione peroxidase (GPx) activity less than 50 U/L. Incidence and severity of apparent WMD were defined in terms of elevated plasma activities of creatine kinase (CK) or aspartate aminotransaminase (AST). Of the weaner flocks, 58% (22/38) had mean plasma vitamin E concentrations in the deficient range (<0.7 mg/L) and 50% (19/38) had mean CK activities above 400 U/L (mild WMD); four of these flocks had mean CK activities over 1200 U/L (severe WMD). Of all the individual weaner sheep sampled, 6% had plasma CK activities >1200 U/L. It is likely that the incidence of vitamin E deficiency would have been higher had it not been for unseasonal summer rain germinating pasture on eight of the survey farms in the northern wheat belt. Flocks from farms with an evident green flush to their pastures had higher vitamin E levels than flocks grazing dry pasture. Vitamin E deficiency was less common in adult sheep than weaner sheep, with only 16% of flocks (6/38) having mean plasma concentrations below 0.7 mg/L and 11% (4/38) with CK values above 400 U/L. Selenium deficiency was less common than vitamin E deficiency and was mostly confined to adult flocks, with only 5% (2/38) of these having mean GPx values below the critical value of 50 U/g haemoglobin. For both weaner and adult sheep classed as vitamin E deficient, CK and AST activity in plasma was best described by a combination of plasma vitamin E concentration and whole blood activity of GPx (significant linear step wise regression, P < 0.001). The present study shows that subclinical vitamin E deficiency (<0.7 mg/L) was widespread in weaner flocks in WA during autumn and that, based on the biochemical data, deficiency was associated with apparent severe muscle damage in 6% of weaner sheep sampled. Recommended strategies to treat weaner sheep showing signs of WMD include dosing with 2000–4000 mg vitamin E either by injection, oral drench or by spraying it onto supplementary grain. The level and frequency of dosing depends upon the severity of the WMD symptoms. Less is known about preventative treatment, but recent evidence suggests that providing weaner sheep with access to saltbush during autumn may prove to be a practically useful strategy. Selenium supplements should also be supplied to weaner and adult sheep in areas known to be selenium deficient.
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