The latest 3.5% decline in Fonterra's fortnightly Global Dairy Trade auction brings the cumulative fall in the average price to 25% since May.
The fall was the 16th out of the past 19 auctions and calls into question whether Fonterra can maintain its current forecast payout of $6.25 to $6.50 a kilogram of milk solids, or cut it further.
The overall GDT price index dropped 3.5% from a fortnight ago, with the average price falling from $US2851 ($NZ4199) a tonne to $US2727 ($NZ4018).
Craigs Investment Partners broker Peter McIntyre said the headline index fall of 3.5% brought the cumulative decline in average pricing to 25% since May.
The key product group, whole milk powder, fell 1.8% to its lowest point since August 2016.