A lack of rain over December and early January meant winter feed crops in Southland and southern and coastal Otago had lost up to two growing months, Federated Farmers adverse events spokesman David Rose said.
Federated Farmers and DairyNZ were working together to ensure farmers in those areas could source adequate feed for their stock.
"Naturally, we're all hoping for a benign autumn which will allow winter feed crops to achieve better yields. However, many farmers are sourcing supplies to make sure they don't run short in winter and we are looking to help," Mr Rose said.
Those farmers needing feed and those with surplus feed could call 0800-376-844 to add listings to the feed-needed or feed-available lists. It was open to all farmers, not just dairy farmers.
Once the feed types available had been collated, the information would be posted on the federation's website www.fedfarm.org.nz.
December was the driest month on record for most of Southland, with as little as 3% of the historical average rainfall in some parts.
DairyNZ Southland-Otago regional leader Miranda Hunter urged farmers to "do the numbers and put a plan in place".
"If that involves accessing extra feed and grazing, they need to get on to it," she said.
A lot of winter crop was sown late because it was wet in November, but then it got dry and crops had been slow to germinate because of low moisture levels.
There was also a lot of multi-striking, with plants striking over a range of times, rather than over a short period, which could be an issue in terms of weeds and pests.
"Obviously, crops are not as good as they could be," she said.
Normally, farmers would make up the shortfall of crops with extra supplements, but they did not have large amounts of supplements on hand because of the dry summer, so they were looking at sourcing supplements or for alternative grazing arrangements.
While the lack of feed in the South was "reasonably serious", a positive aspect was it was not a South Island-wide situation, with North Otago and Canterbury having had a good season.
Those regions were providing options - whether selling feed or providing grazing.
It had not been a great season for many people and they needed to "ring fence" the impact into this season. They should also talk to their bank manager if necessary.
Obviously, quite a few farmers were not going to produce the kilograms of milk solids they initially thought they were going to and their costs were also going to be higher, she said.
There were also going to be a lot more stock movements this year and farmers needed to remember to book trucks for transport.
Mossburn dairy farmer David Holdaway, who has already sourced grazing, said a lot of winter feed crops in Southland were not up to their usual stage.
While there was a shortfall in Southland, it was not going to be very serious because it was offset by a lot of feed further north, he said.
Wayne Nichol, from PGG Wrightson Seeds, encouraged farmers to check their feed supplies and do their budgets.