An Inangahua dairy farmer whose milk was sabotaged with penicillin earlier this month will still have to pay Westland Milk Products upwards of $7000 for a tanker load of tainted milk that had to be poured down the drain.
Police are investigating the deliberate contamination.
Constable Graham Kimber of Reefton police confirmed today inquiries were focused on a disgruntled farm worker.
The contaminated milk was pumped into a tanker laden with milk from other farms in the area, and then trucked back to the processing factory in Hokitika.
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Westland Milk Products chief executive Rod Quin said the tainted milk went into a 12,000-litre tanker, even though the contamination was not his fault.
However, if it was found that the milk had been ruined by a "disgruntled farm worker, for example'', the farmer might be able to claim the cost through his insurance.
"The contamination of any food deliberately is not welcome anywhere in this country,'' Mr Quin said.
"The presence of an inhibited substance was identified in the milk as a result of our rigorous raw milk testing procedures. We take any potential contamination of our milk very seriously and undertake mandatory testing of all milk product before it leaves the farm gate.
"In this particular instance, the addition of antibiotics was identified and the affected milk segregated accordingly,'' he said.
Penicillin is used on many farms to treat cows that have infection or illness.
Federated Farmers West Coast president Katie Milne said yesterday it would have taken only a syringe full to be squirted into the tank to contaminate the entire batch.