Meanwhile, a near 5 per cent fall in the New Zealand dollar since September has provided some offset.
"However, the full benefit of the New Zealand dollar is unlikely to be reflected in this season's milk price, however next season's stands to gain more fully," Penny said.
The dairy market outlook has also weakened over the same period.
In particular, global production has improved, Penny said. "Moreover, New Zealand weather and production have recovered somewhat after the very wet spring."
The current dry weather is starting to pose a risk to New Zealand production, economists said.
At this morning's GlobalDairyTrade auction, the price of whole milk powder (WMP) - a major component of Fonterra's milk price forecast - rose by 1.7 per cent to US$2830 a tonne, partly reversing a downward trend.
WMP prices have been falling sharply since September 20, when it traded at US$3122 a tonne. -- Staff Reporter