Effects of organic and inorganic sulphur on the availability of dietary copper to sheep.

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. Sulphur compounds are broken down extensively by rumen microflora to yield sulphide (Anderson, 1956; Bosman, 1965, 1966) and it has been suggested that the subsequent formation of insoluble copper sulphide in the rumen lowers the avail-If this hypothesis is valid, one would expect the availability of Cu to decrease as S intake increases and organic S and inorganic sulphate to have similar effects, since both are readily degraded to yield sulphide (Bosman, 1965; Hume & Bird, 1970). It is also possible that the Cu status of the grazing animal will be determined in part by the S content of the pasture, which commonly ranges from 1.0 to 4.0 g/kg dry matter (DM) (Whitehead, 1966). There is at present insufficient experimental evidence with regard to the influence of dietary S on the Cu metabolism of ruminants. The effects of organic S have not been studied despite the fact that some 60-70% of the S in herbage exists in the organic form (Furrer, 1966; Hartmans, 1970) as …