At that level, though, the majority of farmers would still be in the black, Penny said.
At the last GlobalDairyTrade (GDT) auction whole milk powder - a key driver of the milk price - traded at US$2833 a tonne - down 10 per cent on its June traded price.
Earlier this month, Fonterra announced a revision to its forecast for the 2017/18 just passed, shaving 5c off the price to $6.70/kg in order to support the co-op's balance.
Milk is Fonterra's biggest input cost and high milk prices, while beneficial to farmers, can hurt the co-op's bottom line.
Fonterra's balance was already under pressure from the legal settlement to French food group Danone and the impairment of its investment in China's Beingmate.
The co-op said at the time that $6.70/kg remained a strong milk price, historically.
The next GDT auction is due on Wednesday.
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