Copper, iron, manganese and zinc concentrations in the carcases of lambs and calves and the relationship to trace element requirements for growth.

I . The minced carcases of twenty-seven lambs, ranging from 18 to 69 kg in live weight, and twenty-five calves (30-90 kg) were analysed for copper, iron, manganese and zinc. The lambs were weaned whereas the calves were reared exclusively on milk. 2. Mean concentrations of Fe, Mn and Zn for groups of lamb carcases fell within the ranges 52.6-75.1, 0.7-1.2 and 20.8-25.6 mg/kg fresh carcase weight respectively. The concentrations of Fe and Mn decreased while that of Zn increased slightly with age at slaughter. The concentrations of Fe, Mn and Zn in calves were close to those in lambs. 3. For both species, the concentration of Cu in the carcase vaned erratically: variation in hepatic Cu storage was implicated. In an additional study of ten full-term foetuses from Cu-depleted or Cu-supplemented ewes, a dietary Cu supplement (10 mg/kg dry matter (DM)) increased foetal Cu status 10-fold, due largely to an increase in foetal liver Cu. 4. The mean retentions of trace elements in the lamb carcases (yo intake) were approximately: Cu 2.0, Fe 1.3, Mn 0.08, Zn 4.0. The corresponding values for the milk-fed calves were all probably much higher (Cu 23, Fe 43.7, Mn 4.9, Zn 34.0) but Cu intake was not accurately measured. 5. After allowing for tissue storage of Fe and Mn, values of 55,o.Q and 24 mg/kg carcase gain were taken to represent the approximate net growth requirements of lambs for Fe, Mn and Zn respectively: the corresponding value for Cu was probably < 1.0 mg/kg. Values for calves were similar to those for lambs. 6. It was concluded that the total net requirements of ruminants for Fe and Zn should be considered in terms of daily intakes of the metals rather than dietary concentrations because of the relatively large and constant contribution of the growth component to the total requirement.