"Climatic conditions have quickly turned from very favourable settings in August, and are now a significant headwind for milk production," it said.
"All regions are impacted, in particular the North and West of Victoria, where widespread flooding has impacted dairy herds and pastures," the company said.
The company said it was continuing to work with industry stakeholders to ensure our supplier base and industry are taking appropriate action to address these conditions.
Murray Goulburn is Australia's largest dairy foods companies and one of Australia's largest food and beverage companies with annual turnover of about $2.8 billion. The co-op has about 2,200 supplier shareholders.
The co-op's units, which trade on the ASX, were quoted at A$1.15 - down four cents from Wednesday's close.
Fonterra this month said wet weather had taken a heavy and "highly unusual" toll on Fonterra's milk production as the season heads towards its peak.
"These decreases have been made in response to significant reductions in daily milk
volumes across the central and upper North Island in October, particularly the key dairying region of Waikato where early October daily milk volumes have been down around 10 per cent versus the same time in the 2015/16 season," Fonterra said.