Dairy commodity prices slipped at Fonterra's overnight online auction, with the globalDairyTrade trade weighted index down 2.5 per cent from the previous auction.

It was the second decline in a row, following a fall of 1.3 per cent a fortnight ago. The average winning price overnight was US$3506 ($4708).

For anhydrous milk fat, the average price fell 1.2 per cent overnight to US$5196, butter milk powder was down 1.1 per cent to US$3033, skim milk powder fell 4.7 per cent to US$3072, and whole milk powder slipped 1.1 per cent to US$3484.

See more details of the auction here.