Wet weather could lead to problems when trying to breed cows this spring, DairyNZ is warning farmers.
DairyNZ senior developer Mark Blackwell said missing or wrongly identifying cows on heat could cost farmers thousands of dollars each year through reduced in-calf rates and later calving patterns.
The weather could dampen pregnancy rates in cows.
"The cows tend to express heat less vigorously and are harder to detect on heat in these conditions.
"They're [farmers] just going to need to be really vigilant in the first three weeks, especially when they're heat detecting for artificial breeding."
If farmers had a lower pregnancy rate among their cows, or cows that calved later next year, that could hurt their bottom line, Mr Blackwell said.
"It does have [an] economic impact - reports I'm hearing are that situations on farm are quite variable.
"Rather than worry about it they should get out and make sure they are doing everything proactively."
Some options to help reduce cow stress include once-a-day milking, or increasing feed supplement. Mr Blackwell said farmers should get advice if they were considering changes.
"It pays to get a second opinion as it can be hard to assess your own farm situation objectively."