About 3500 litres of fresh milk may have been deliberately sabotaged, after penicillin was discovered in the product.
The alleged attack is believed to have occurred at the Inangahua Buller dairy farm in the north west of New Zealand’s south island and was detected during routine testing at the Westlands Milk Products factory in Hokitika.
Reefton police are investigating whether the penicillin, which is used on the farm to treat cows, could have been deliberately added to the milk.
The farmer alleges that a person came onto the farm and dropped the antibiotic in the product on purpose, but Constable Hraham Kimber told stuff.co.nz that there are no suspects at this stage.
"It’s a hard thing to prove unless you have seen it happen," he said.
The raw milk was worth about $NZ2000 but the dairy farmer could be liable for excess costs, because it was collected by a tanker which was carrying 12 000 litres, worth $NZ8000, which had to be dumped because of the contaminated milk.
Penicillin is only dangerous in very high doses or to those that are allergic.
Federated Farmers West Coast president Katie Milne told the Greymouth Star she was shocked by the incident.
"It’s a disgusting thing to do and I hope the culprit is caught and the police come down hard on whoever did it."