In this chapter, the factors that affects mineral absorption in livestock as well as ways of controlling mineral intake in animals are discussed. Topics include: selective grazing, diet selection, clinical and pathological changes, biochemical indicators of mineral deprivation, differentiation of mineral deprivation, criteria of dysfunction, physiological and developmental effects, functional forms and indices, correction of mineral imbalance, mineral supplementation, and mineral sources.

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I . The effects of dietary sulphur on the availability of dietary copper were estimated by means of a repletion technique. The responses of initially hypocupraemic ewes to repletion with Cu-supplemented diets containing supplements of organic S, as methionine, and of inorganic S, as Na,SO,, were compared with those obtained with a diet low in S.2. The two forms of S had similar effects. Responses in plasma Cu were reduced by 3 9 3 6 % when S was increased from 1.0 to 3.0 or 4.0 g/kg diet and the availability of dietary Cu was estimated to have decreased from 0.062 too.041. Both S supplements produced marked increases in rumen sulphide concentrations.3. Dietary S had no effect on plasma Cu when added to the low-Cu diet of hypocupraemic ewes being repleted by a continuous intravenous infusion of Cu.4. The addition of CuS, providing 5 mg Cu/kg, to the diet of hypocupraemic ewes produced no response in plasma Cu or haemoglobin. The same amount of Cu, given as CuSO,, increased plasma Cu by 0.46k0.15 mg/l and haemoglobin by 33 f3.8 g/1 after 36 d: the subsequent replacement of CuSOl by CuS induced hypocupraemia again but had no effect on haemoglobin. 5.It was concluded that variations in dietary S within the normal range for herbage exert an independent effect on Cu metabolism, possibly through the formation of insoluble CuS at sites beyond the rumen.

The aetiology of copper deficiency in grazing ruminants has been clarified by a number of recent discoveries: the low availability of copper in lush grazed pasture compared with conserved forage; the inhibitory effects on absorption of small increases in herbage molybdenum and sulphur and the antagonism from iron ingested in soil; and the wide genetic variation in copper absorption between different breeds of sheep. The economic importance of copper deficiency has been emphasised by the discovery of unsuspected causes of loss: increased susceptibility to infection and growth retardation in lambs and infertility in cattle. The diagnosis of functional copper deficiency has been improved by the addition of erythrocyte superoxide dismutase to the assays of copper status.