Global dairy prices dropped more than 5% at Fonterra's latest fortnightly auction, the third consecutive fall.
The average winning price in the auction on Tuesday night was $US4,443 per metric tonne.
Whole milk powder prices fell more than 7%, anhydrous milk fat was down more than 4% and skim milk powder and butter prices were also weaker. Butter milk powder rose 3.3%.
Prices began falling in mid-April after nine consecutive rises.
Volumes have increased substantially from previous sessions when supply was tight due to the drought.
Last week, Fonterra increased its next season forecast payout to farmers because of the recent squeeze on supplies.