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SUMMARY Culled dairy cows were studied during starvation prior to slaughter to determine the metabolic changes related to the development of the ‘downer’ condition. Of 200 apparently normal cows, 23% had hypocalcaemia, 33.5% had hypomagnesemia and 12.5% had both on arrival at the abattoir. Cows which became ‘downers’ had significantly lower serum calcium concentrations, were in better body condition, were at a later stage of pregnancy, and their carcases had a significantly higher ultimate pH of M. longissimus dorsi than ambulant cows. In cows more than 6 months pregnant serum calcium concentration decreased markedly during the 2 days after arrival at the abattoir, but then increased and was similar to that of non-pregnant cows and cows less than 6 months pregnant after 3 days. Some cows were unable to make this adjustment and usually became ‘downers’ within 3 days of arrival at the abattoir. Measurements of the ultimate pH of samples of M. longissimus dorsi of carcases of cows starved for 7 days before slaughter showed that cows more than 6 months pregnant had significantly higher values than non-pregnant cows. It was concluded that the metabolic changes could be minimised and the incidence of ‘downers’ reduced by avoiding prolonged periods of starvation. Losses may be reduced by preferential slaughter of cows late in pregnancy, and by parenteral treatment of affected cows in the initial stages of the ‘downer’ condition.