Over the past seven days Oamaru has experienced 91mm of rain, and the Dasher 140mm, which has increased health problems for cows and placed extra stress on farmers working hard at the start of the calving season.
Oamaru veterinarian Mat O'Sullivan said the wet weather had a direct impact on an increase in animal disease over the past week.
"Major concerns for farmers are that cows just aren't able to get enough dry matter intake, and that they are also causing quite a lot of damage to their pastures, so cows start pugging pastures.
"As far as animal health concerns, there has been an increased rate in mastitis, which is an infection of the mammary gland, as that's brought about from, basically, contamination of the cakes with mud and dirty water."
Although calf losses to date had been low, Mr O'Sullivan said a feed shortage due to wet weather would have a further impact on calves in the coming weeks, due to a lack of colostrum transferred from mother to calf.
North Otago Federated Farmers president Richard Strowger said farmers were already working round the clock calving, and the wet weather had made life "difficult" for farmers and animals.
"It's an added stress. It's a busy time of year - cows are calving and when the weather comes in like this, it puts metabolic issues on to cows. They go down with milk fevers and magnesium and all the rest of it.
"Because it is so wet and horrible, the cow doesn't eat enough, and then she loses energy when she has the calf inside of her."
He added that a combination of tiredness and bad weather could also cause accidents on the farm.
"What happens sometimes, when it is raining hard, the person riding the bike has his head down and he can go the wrong direction ... It is a dangerous time to be driving, because people are tired.
"You have animal health issues so people tend to work right through [the night] to make the animals as comfortable as they can, which makes more work for everyone."
To add to farmers' woes, a total of 21 flood-affected rural roads in Waitaki yesterday remained closed.
