The average price at the auction fell 4.2 percent to $US2836 ($NZ4747) a tonne.
Most of the products offered fell in price, but dairy powders were markedly lower.
The price of whole milk powder, which strongly influences the payouts for local farmers, fell 3.9 percent to $USD2707 a tonne.
That is the weakest since January last year, and below the break-even point for many farmers.