Copper metabolism in growing sheep given kale (Brassica oleracea) and ryegrass (Lolium perenne)–clover (Trifolium repens) fresh forage diets

Abstract

1. Kale (Brassica oleracea) and ryegrass (Lolium perenne)–clover (Trifolium repens) pasture grown under similar soil conditions were grazed in the vegetative state by growing lambs of 23·6 kg initial live weight for 24 weeks. Forty-eight lambs grazed each forage. The kale and pasture contained respectively 4 and 14 mg copper/kg dry matter (DM), 7·2 and 3·1 g total sulphur/kg DM and 0·4 and 1·1 mg molybdenum/kg DM.2. Subcutaneous injections of Cu (12 mg) were given to half the animals grazing each forage during weeks 1, 6, 12 and 18.3. All ninety-six animals were slaughtered at the end of the experiment and an additional group of twelve animals was slaughtered when the experiment commenced. Liver Cu was determined on all slaughtered animals and heart muscle cytochrome oxidase (EC1.9.3.1) activity on those slaughtered at week 24. Blood samples removed at 6-week intervals were assayed for activity of superoxide dismutase (EC1.15.1.1; SOD) and serum Cu concentration determined. Wool growth, live-weight gain and cytochrome oxidase activity of biopsied hind-limb muscle were also measured at 6-week intervals.4. Control animals grazing pasture showed an accumulation of total liver Cu during the experiment. Animals grazing this diet and given Cu injections showed an additional accumulation of liver Cu equivalent to the supplementary Cu administered, but Cu supplementationdid not affect the activity of any of the Cu-containing enzymes measured and did not affect live-weight gain or wool growth.5. Control animals grazing kale showed a depletion of total liver Cu and reductions in serum Cu concentrations during weeks 18 and 24. However, cytochrome oxidase activity inheart and hind-limb muscle was similar to that of pasture-fed lambs. Blood SOD activity was reduced by kale feeding, but a laboratory study showed this enzyme was not inactivatedby dimethyl disulphide produced from rumen fermentation of S-methyl-L-cysteine sulphoxide(SMCO) which occurs in kale.6. Cu supplementation of kale-fed lambs had no effect on hind-limb cytochrome oxidaseactivity, but considerably increased total cytochrome oxidase activity in the heart and minimized the reduction in blood SOD activity. Both are considered to represent defence mechanisms against the haemolytic anaemia caused by SMCO. However, Cu supplementation did not affect live-weight gain or wool growth.7. The proportion of injected Cu not recovered in the liver at slaughter was greater for lambs grazing kale than ryegrass–clover pasture and the same result was calculated from Barryet al.(1981) for growing cattle. It was therefore concluded that Cu requirements must be greater for growing sheep and cattle grazing kale than ryegrass-clover pasture.