1. Introduction Table 1.1: Recommended minimum element ...

1 (1) element supplementation of grazing animalsand pastures has produced spectacularimprovements in the productivity of sheep, beef anddairy enterprises in Victoria. This fact is widelyknown to farmers, and interest in the use of traceelements is further stimulated by suppliers of a widerange of trace element remedies, licks, mineraladditions and there is a tendency among farmers andothers to assume that if pastures or livestock are notthriving, then the cause must be trace mineraldeficiency. Such an assumption can be quitemisleading. Compared with other soil fertilityproblems, drought, underfeeding and parasitism,trace element deficiencies are not the major causeof unsatisfactory productivity of pastures andgrazing animals in southern is essential that pasture or animal problems beinvestigated by professional advisers skilled in themineral requirements of pastures and livestock andsupported by competent field and analyticallaboratory requirements of livestockMinerals required by livestock are classified aseither macrominerals or trace elements.

2 On the basisof the quantities macrominerals (average daily requirement ingram amounts per head) are needed for structuralpurposes (calcium, phosphorus, sulphur), in themaintenance of osmotic and acid-base balance(sodium, potassium, chlorine) and as contributors toenergy transfer, nerve impulse transmission, andnormal enzyme activity (potassium, calcium, mag-nesium, phosphorus).The trace elements (average daily requirement inmicrogram amounts per head) act primarily ascatalysts in enzyme systems. They function eitheras co-factors (manganese) or by contributingstructurally and functionally to the activities ofenzymes (zinc, copper, molybdenum, selenium),hormones (iodine) or vitamins (cobalt).

3 It is important to note that while the informationpublished in textbooks and requirement statements(ARC 1980, Grace 1983, NRC 1978, Underwood1981), summarised in Table , is useful for pre-paring feed mixtures, it is really of limited use inassessing the mineral nutrition of grazing the actual amounts ingested, nor theavailability of the minerals in the diet, can bepredicted with sufficient accuracy. Seasonalchanges in pasture growth and mineral composition,selective grazing, and pasture shortages due todrought or high stocking rates, make it difficult topredict mineral intake in extensive.

4 Recommended minimum elementconcentrations in pasture dry matter for grazingcattle and sheep1 CattleSheepMacromineralsg/ elementsmg/kgmg/kgIron4040 Zinc2520 Manganese2525 Copper25 to Based on data presented by the ARC (1980), Grace(1983), NRC (1978), Underwood (1981) these amountsrepresent the average requirements for growth, pregnancyor lactation, in grazing Copper requirements are strongly affected by theconcentrations of molybdenum, sulphur and to assess trace element nutrition inlivestockA range of laboratory tests has been developed toprovide a practical means for assessing the traceelement nutrition of pastures and grazing tests on diets (pasture andsupplements), body fluids (blood, urine, saliva) andtissues (liver, bone)

5 Have been devised for theassessment of nutritional status of is important to emphasise that these biochemicaltests assist in the determination of trace elementnutrition, but are not substitutes for the traditionalapproach of investigating broader health andproduction problems which may be more definitive diagnosis can be made only frommeasured improvements in health and production ofanimals following supplementation. However,carefully controlled response trials cannot always beconducted on farms and predictions of likely benefitsfrom supplementation may have to be based oninformation relating production responses to theresults of biochemical tests of nutritional range of biochemical indicators ( Table )provides a practical means for assessment of traceelement status of animals in a flock or herd.

6 Theseindicators and their values are tabulated in thechapter on each trace element .(2) Table : Recommended biochemicalindicators for detection of traceelement deficiencies in livestockMineralComponentCopperLiver copperPlasma copper andceruloplasminErythrocyte copper andsuperoxide dismutaseDietary copper, molybdenum,sulphurCobaltLiver vitamin B12 Plasma vitamin B12 Dietary cobaltSeleniumBlood glutathione peroxidaseLiver seleniumDietary seleniumIodineMilk iodineThyroid iodine contentManganeseDietary manganeseZincPlasma zincDietary requirements for pastureproductionAt least 15 mineral elements are considered to beessential for plant macrominerals (present in g/kg concentrations)

7 Are nitrogen, phosphorus, potassium, calcium,magnesium, sodium, chlorine and trace elements (present in mg/kgconcentrations) include manganese, iron, copper,zinc, molybdenum, boron and cobalt (Grace 1983).Stimulation of growth has been reported foraluminium, arsenic, chromium, fluorine, iodine,lithium, selenium and titanium, but the evidence isgenerally inconclusive and most of these elementsare more commonly known for their toxicity to plants(Sauchelli 1969).While the roles of the macrominerals in thephysiology of plants is generally well understood,those of the trace elements is much less so.

8 Plantsrequire minerals for protein synthesis (nitrogen,sulfur), structural purposes (calcium, magnesium,boron), photosynthesis (magnesium, iron,manganese, molybdenum, chlorine), energy transfer(phosphorus), enzyme activity (potassium, calcium,magnesium, copper, zinc, molybdenum), cell turgorand cation-anion balance (potassium, calcium,magnesium, sodium, manganese) and nitrogenfixation in legumes (molybdenum, cobalt, iron).The minimum concentrations of minerals in plantsrequired for maximum growth have been determinedfor many elements using nutrient solution culture(Chapman 1966, Loneragan and Snowball 1969,Asher and Ozanne 1967).

9 However, theseconcentrations may be considerably lower than thoserequired for optimum yield in the field ( Table ).Plants in solution culture do not have to overcomethe effects of various environmental stresses such ashigh manganese, salt and low oxygen in the rootzone, high transpiration rates and grazing pressureas occurs in the plant species and cultivars have differentrequirements for a mineral . Soil deficiencies cantherefore influence the botanical composition ofpastures as well as their : minimum element concentrations inwhole tops of subterranean clover for itsoptimum growthTrace Tests to assess trace element levels inpasturesSoil and plant tests can be useful aids in theformulation of fertiliser recommendations to improvepasture testing attempts to represent the quantity ofelement that is readily available to the around the world use different soil test(3) be useful the soil tests must have been calibratedwith growth responses in local field trials because oflikely soil and other environmental differences.

10 Forelements such as potassium and phosphorus,departmental soil testing methods have been foundto be quite useful; but soil testing has not been usefulfor most other elements, particularly the small concentrations and the variety of chemicalforms of trace elements in the soil, plus themultiplicity of factors that may affect their availabilityto plants, make soil tests for trace elements verydifficult to interpret. For example, soil copper analysisis no longer available from this Department becauseresearch over many years indicated that thecorrelation between soil copper (EDTA Cu) andcopper deficiency in both pastures and livestock waspoor (Conley 1983).