Data were obtained on 32 Holstein calves aged 2-5 days, 30 similar calves aged 20-30 days, and 30 similar calves aged 50-60 days. For the 3 groups respectively, iron concentration (μmol/litre blood serum) averaged 26.1, 14.0 and 25.3, and haemoglobin concentration (g/litre) 91.30, 51.42 and 95