Fifty-thousand litres of milk was drained out of a vat in one of several instances of farm vandalism over the long weekend.
Police were investigating the burglary at a farm in Leeston, Canterbury.
Holes were also punctured in 30 irrigator tyres at another farm in Hororata.
Federated Farmers mid-Canterbury president Michael Salvesen said there was some tension between urban and rural communities during the election period, but it was not clear whether the vandalism was related to that in either case.
Farmers were feeling "picked on", he said.
"They try to do a decent job and almost all farmers care for their properties immensely so it's very upsetting to see when these things happen."
The vandalism highlighted the importance of on-farm security, Mr Salvesen said.