Dairy prices fell across the board for all products at Fonterra's latest global auction which took place overnight.
The average selling price was down 1.8 percent from a fortnight ago to $US3873 per tonne. Volumes were also down by 4500 tonnes.
Prices have fallen 23 percent since reaching a record high $5042 a tonne in early February and are the lowest since February 2013.
Prices for whole milk powder, which is the largest amount of product sold, fell 1 percent to $US3877, skim milk powder by 3 point 5 percent to $US3733, butter by 3.8 percent to $US3667, cheddar by 2 .1 percent to $US4108, and butter milk powder by 1.9 percent to $US3940.
That offset price gains for anhydrous milk fat, which rose 1.9 percent to $US4255 and rennet casein by 4.6 percent to $US11,861.
It was the seventh consecutive decrease in auction prices and the lowest selling price since February 2013.
Rabobank of dairy research director Hayley Moynihan said the fall was to be expected.
The New Zealand dollar fell to US85.6 cents.