Federated Farmers president Don Nicolson, who runs a farm south east of Invercargill, says he's lost four times as many sheep this year as he would in a normal year.
The heavy snow overed parts of Southland at the weekend came at the height of the lambing season.
There have also been heavy rain and strong winds. More snow is expected to fall on Monday night.
Mr Nicolson says the snowstorm is the worst he has ever seen and his sheep stocks have fallen 15%, four times more than the annual average.
He said some areas are already covered in up to 30cm of snow and with more snow forecast, many more sheep may die.
He says farmers are trying to get calcium and magnesium as well as glucose into the more susceptible animals.