To measure any between-animal differences in requirement of energy for maintenance of cows 38 metabolic balance trials were performed with 13 dry Friesian cows in their 7th month of pregnancy, on the same rations. For 6 of the cows measurements were also taken in the 9th month of pregnancy. A detailed description was given of new respiration chambers used and of techniques. The results of 237 balance trials with cattle with an energy balance between + 4000 and - 4000 kcal. described in the literature, were analysed statistically. In this material between-animal variation in metabolizable energy for maintenance, corrected to the same bodyweight, reached about 11 % and within some breeds 8- 10 %. In the author's trials, variation in Friesians was 4-8 % similar to results of published trials. For both sets of data a reliable figure for between-animal variation needed exclusion of such factors as differences in ration, date of measurement and pregnancy. From the author's trials utilisation of metabolizable energy for growth of foetus, foetal membranes and udder was about half of that for fattening if it was assumed that pregnancy had no influence on maintenance requirement.
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