About 20 years ago, I received a phone call from a schoolgirl in Swindon who asked if she could come and milk cows for me, as she wanted to become a vet.

At first, she planned on being a small-animal vet, but after spending weekends working on the farm, she became determined to focus on large animals, mainly cows.

Such was her determination that she is now fully qualified, practicing in north Wales and has even made regular trips to London to discuss the TB situation with government bodies.

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Recently, I had the opportunity to spend an evening with her and hear her current thoughts. She firmly believes that inconclusive animals should either be slaughtered or kept separate.

I suggested there might be a possibility that an inconclusive result could indicate an animal had been exposed and was now recovering.

Lively debate

This sparked a lively debate: she argued that has never been known to happen, while I pointed out that nobody has ever properly studied the situation or the scientific circumstances.

She also stated that farmers should not be given post-mortem results. She argued that they are inflammatory and misleading.

She explained that TB is a very difficult bacteria to culture and that some TB lesions are as small as a grain of rice.

She also explained that the chance of a false positive result from the skin test at standard interpretation is one in 5,000.

No visible lesions at post-mortem means either the animal was too early in the disease process for lesions to have developed or that lesions were so small, they could not be picked up by the human eye. No visible lesions does not mean no TB.

Tests available

She then explained the different available tests. The first is the skin test, which we are all familiar with, though its reliability is quoted as somewhere between 60% and 80%.

She also explained her theory that we should pay more attention to bovine lumps. Bovine lumps with an increase in size of greater than 2mm are red flags.

Even if they technically pass the skin test, they are risky animals. Cull them or adopt a policy of not breeding replacements from them.

The next test is the gamma interferon test.

I told her I understood this to be “100% to 120% accurate” and eliminates false negatives. She quickly corrected me, saying that it did not completely eliminate false negatives, but did increase the proportion of true positives compared with the skin test due to higher test sensitivity compared with the skin test.

She also advised me that no test can be more than 100% accurate, because if a test picks up all infected animals and leaves behind all uninfected animals, then it is 100% accurate.

Any deviation from that (for example a false positive or a false negative) means it is less than 100% accurate.

There is also a third test, which, she explained, could remove a significant number of false positives.

I asked her if, by paying privately, I could use this test and then be exempt from slaughter on the basis of it. She replied “definitely not” - which seems a very unfortunate situation.

We currently see Jeremy Clarkson facing the reality that his herd has gone down with TB. I feel extremely sad for him.

But it also highlights what farmers go through - turning a problem that is statistical for us into an emotional one for the general public.

Digester

On another front, something else has been irksome.

Just four miles away, there is an estate with 3,000 acres of maize destined for a bio-digester. I am about to contact my MP to ask her to approach the company and suggest that some of this acreage be linked to local farmers.

Surely it would be greener to feed some of this maize to our cattle rather than transporting feed from 100 miles away or, worse, sending animals to slaughter unnecessarily.

After all, it’s no good opening the fridge door, seeing the light come on because you’ve got electricity from a digester, but then finding no dairy products inside due to shortages.