In the present study, milk secretion was slightly reduced by leaving 30% of the milk in the udder (treatment 70%): 1.6 kg less milk was produced between M0 and M1 milkings. Ultrasonography performed just after the M0 milking showed increased cisternal area for this treatment, meaning that milk left in the udder at M0 was at least partially present in the cistern. This could explain why cows exhibited small reductions in milk yield in response to such incomplete milking. If this 30% of milk left unremoved was stored exclusively in the alveolar compartment, the negative effect on milk secretion would have been increased. For example,