Overall, dairy prices fell 0.3%, and while most products posted falls, whole milk powder - New Zealand's key export - bucked the trend and increased for the second consecutive auction.
ASB economists said time was ''fast running out'' for farmers for the 2014-15 season's milk price.
While a weaker New Zealand dollar was helping, prices needed to lift materially over the coming auctions for the bank's $5.10 forecast to hold.
In September, Fonterra dropped its forecast by 70c to $5.30.
While whole milk powder might have ''found a bottom'', the search for a bottom for broader global dairy prices continued, ASB rural economist Nathan Penny said.
That reflected the global excess of milk more generally, while New Zealand production and export growth slowed from its frantic pace earlier in the year.
The other factor in play might be Fonterra's ''careful management'' of auction volumes. It looked to be holding back volumes over recent auctions relative to production, he said.
Mr Penny described the 0.3% fall as ''neither here nor there'', saying it reflected falls for six products just about being offset by the rise in whole milk powder prices.
Cheddar led the way in the price falls, down 9.2%, while butter and buttermilk powder also posted chunky falls, down 4.1% and 6.9% respectively.
Prices for near-dated contracts remained low, while longer-dated contracts pointed to potential price strength in the new year.
Whole milk powder contracts for delivery in four and five months lifted more than $US160 and $US230 a metric tonne from the previous auction.
Westpac senior economist Michael Gordon said the further drop in prices for skim milk powder and especially for value-added products such as cheese, suggested that Russia's ban on imports from many Western countries was still weighing heavily on the global market.
Looking further out, ASB remained confident that beyond the short-term over-supplied situation, the market would be more balanced and prices would settle at a higher level. It continued to maintain its 2015-16 forecast of $6.50 and a long-run forecast of $7.
