Negative TB test doesn’t mean no TB

The headline says: Otago dairy herd to be slaughtered after one cow tests positive to tuberculosis.

It sounds like the farmer has no choice and that Ministry for Primary Industries is being unfair.

But he does have choices and the MPI is doing what the law requires and empowers it to do – keeping food safe and people healthy.

Only one cow has tested positive for TB but that doesn’t mean the rest of the herd is clear.

We had some cows test positive for TB a few years after we started dairying. All were slaughtered and vets who examined the carcasses found some, but not all of them had the disease.

The herd was tested again, any cows that were positive were killed and again some had TB and some didn’t.

Eventually the herd got several clear tests in a row but a couple of years later we had another cow test positive for TB.

We went through the culling and testing again until we got the all-clear.

More than a year after that a cow from our original herd dried herself off, was culled and sent to the works. There the vet found she was riddled with TB. She had been tested before we bought the herd, tested again several times on our farm but not once did she react positively.

A vet told us that was because she was too busy fighting the disease to react to the test.

Our milk is pasteurised so there was no danger to anyone if it was infected with TB.

The farmer in the story sells raw milk which is why MPI has said he must stop. TB tests aren’t 100% reliable and there is a risk that another cow in the herd could have the disease and pass it on to people through milk unless it’s pasteurised.

The farmer isn’t without choices, he doesn’t have to kill his cows. He can’t keep selling raw milk but he could get it pasteurised. He could also sell the herd (although the cows will only be on movement control which means they can only be moved to another property owned by the farmer or to slaughter);  but that’s not what the headline suggests.

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