Another minor setback for dairy farmers with prices dropping slightly overnight.

Fonterra's latest Global Dairy Trade Event has seen a 0.3 percent drop in prices.

Despite a 1.4 percent increase at the last auction, there's been a string of negative results in 2014 that have seen prices almost halve since peaking back in February.

It's led to a reduction in Fonterra's forecast payout for the coming season, down to $5.30 per kilogram of milk solids.

Six of the seven product categories on offer dropped in price, with the exception of whole milk powder which was up 1.6 percent.