The aim of this experiment was to examine the adaptation of mammary energy expenditure in response to variations in milk yield induced by modifications of milking frequency. Three lactating cows were milked at 8-, 12-, 16- or 24-h intervals according to a Youden square with 5 periods of 7 days. When milking interval increased, milk yield decreased significantly by 24%, mammary blood flow significantly by 16% and oxygen consumption not significantly by 18%. As a result, the non significant decrease in the mammary oxygen consumption is associated with no reduction of the oxygen extraction but a decrease blood supply to the udder.