The Cow Magnet – Bolus Points for Garrett!

17th May 2016 — 15 Comments

Cow-Magnet-and-Cow copy 2In 2010 I published an article on ‘cow magnets’, but lost it in the great crash of 2013. Judging by questions I see on detecting forums about whether cowpats initiate a signal on metal detectors, I think it’s about time I resurrected that post. Read this and you may realise how a machine may give a signal on a cowpat.

In retrospect, and in my opinion any such signal is best ignored. The results are invariably disappointing and not worth risking the attendant hazards. In the past year I have read about children being hospitalised by E Coli from cowpats in a park and warnings published in the press. The strain of the bacteria is often associated with rural environments that may have been contaminated by animal faeces. Detectorists be aware!

We learn something new everyday is a trite, often quoted, but undeniably true expression. If, like me, you baulk and make an unnecessary fuss every time you have to take another pill, then you might just enjoy this story featuring Tim and Carol Hollamby, detectorists from East Sussex. Tim started his unusual and remarkable story by saying, Let me tell you what happened today ...

Tim works with farmers on the National Sprayer Testing Scheme (NSTS), so when his mobile phone rang late in the afternoon he wasn’t too surprised to see the name of a farmer who owns land on which he detects. Tim initially thought that he might want spares for his crop sprayer or had some sprayer-related problem…but the call proved to be more interesting than that! William Craig, the farmer, was about to release five calves into pasture after giving each a BOLUS – essentially worming tablets. As they were loaded onto the trailer, William noticed a bolus on the floor. Tim said, It was evident that one of the little blighters had ‘sicked’ it up! Which one, though?

I had never heard of the word ‘bolus’ thus it was completely new to me. Tim briefly explained that the bolus is metallic and degrades slowly in the animal’s gut whilst administering, at intervals, a dose of worming medicine. Must remember that word when playing in the next Winter family Scrabble championship. Could prove to be useful!

All was becoming clear. The farmer had called Tim to ask if he thought a metal detector might help to determine the calf that had taken their bolus and find the calf that had coughed up the medicine. Tim didn’t know, but was prepared to give it a go. He rushed the 30 or so miles to the farm brandishing his Fisher F75 and his brand new Garrett Pro-Pointer.

One of the ways in restraining young animals is with a metal cattle crush. For obvious reasons, some other method would have to be found. Also waving a detector along the body of the calf could end up with a spooked animal, snapped machine or a broken arm.

After some thought, they managed to get the calves in a tight line against a building and ran the Pro-Pointer over the stomach area of each animal. An ecstatic Tim exclaimed, “Bingo. It worked! The pin-pointer burst into life. On to the next one and the same result – a positive screech from the stomach through the skin!” And this was the same for the calves two, three and four! The fifth and final calf failed to set off the probe. The farmer was, to use Tim’s phrase, over the moon! With the help of the Garrett probe, they had eventually found the culprit.


Farmer William Craig – picture courtesy Carol Hollamby

Tim thought that manufacturers Garrett might be interested in what had happened so, on his behalf, I contacted them … only to find that their representative was very, very sceptical. He doubted that the Pro- Pointer had worked in this way, citing how detectorists sometimes got a signal when going over a cowpat and other occasions when a false positive might be present. Until this moment, I hadn’t doubted Tim’s story at all – why should I? I must admit that teeny doubts were now invading my brain cell and threatening to scuttle a potentially excellent story. I vowed to find out more about the bolus, especially after speaking to Tim and going over the story with him again in minute detail.

My first port of call was Mr. Google. As you might expect, there is a lot of useful material on the net, but targeted mainly at cattle farmers. There was little information of the sort I was seeking – answers on the size of the bolus and, essentially, the metal content. I needed to try another avenue of ‘research’.

Unfortunately, I was unable to speak with the manufacturers of the ‘Autoworm’ bolus, but had more luck with the main distributors, Pfizer. A bovine vet in their employ told me that the device had a PVC cap segment, five individual cells holding tablets, a corroding central core and metal end weight of sufficient density to prevent regurgitation. I asked if it would be possible to see one, but he was unable to send an example for testing, as it was ‘a prescribed medicine for farmers only’. I needed to get my hands on one and start experimenting with the Pro-Pointer.

After phoning around, one of ‘my farmers’ (detectorist-speak) agreed to let me borrow a bolus and take it home for testing. Despite promising her anything she wanted, Mrs. John adamantly refused to swallow it – which I was secretly pleased about – because it would have meant a visit to the A&E if she had done so! The cigar-shaped bolus is larger and heavier than I ever imagined. It has a length of 3.5”, a diameter of 1”, and weighs 4.5 ounces. I have tried to give some indication of scale by picturing it alongside a blood pressure tablet.


Picture by JW

Not having a friendly and compliant calf either, I had to resort to other methods of testing. I don’t put them forward as scientific results under strictly controlled conditions, but they satisfied me. For my little experiment, I used two different probes with less than fresh IKEA batteries.

‘Air’ tests in the garden (and kitchen) with the bolus heavy metal end presented to the Pointer, made it sound at just over 3” on both machines. To represent the stomach of a calf, we placed the bolus under our armpits and tried again. I was surprised to hear sound and vibration at what I reckoned to be the same distance, if not a little more. I expected that skin and bone would mean that the signal would be dissipated, but this didn’t seem to be the case. It also worked with the bolus at the other side of my ankle. What a surprise!

I conveyed the results to Tim, who was naturally delighted and also the Garrett representative who had originally expressed a less than enthusiastic response. After hearing my evidence, he graciously apologised for initially doubting the story.

I cannot help but think that there may be another market out there that Garrett had never dreamed of. If it ever happens that this new sales opportunity ever takes off, I hope they remember the Tim and Carol Hollamby and their unusual discovery. Full marks to Garrett. After hearing this story, they presented the farmer with a pin-pointer … just in case it ever happened again!

A version of this article was originally published in the UK Searcher magazine.


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15 responses to The Cow Magnet – Bolus Points for Garrett!

  1. That sounds like a lot of bull to me…..

  2. Poor Mrs John… even if the magnet is inserted into the front end of the cow… A fine load of bolus John! A pat on the head! Seriously, a great story John! Cheers!

  3. Nice touch John. May we see many more!!

  4. Interesting and I can believe it as I use my hand held pinpointer to get a precise ID on target location on shallow signals before I dig.

  5. must admit I keep away from pats these days but as a kid we used to throw them at each other. One such event I got a nice steaming one full in the face and had to wash in the river – didn’t get Weil’s disease either.

  6. Interesting. I sometimes detect on a farm come camping site in Somerset. I was intrigued as I kept getting good signals that produced stainless steel cigar-shaped tubes. The farmer explained that these were Bolus tubes. But,I said, you are not a cattle farmer! No, he said, but I do get my manure from the abattoir! They were like the one you have pictured except steel along the whole length.

    • Yes, that sounds right. The magnet stays in the stomach … until the end. Figures that they should be found in manure from the abattoir.

  7. A pat on the back for that one John!

  8. Brilliant post, John. I suppose that means you can’t take your pet cow on holiday with you. It would never get through security at the airport.

  9. A couple of years ago I got a call from a farmer to run the detector over his Jack Russell. The offending canine had chewed up a tin of dog food & the farmer was concerned that some tin may have been swallowed. This was anything but easy with the dog going absolutely berserk but was finally achieved with the farmer suspending the dog from a leash. Not something the R.S.P.C.A would have approved of but it did the trick & to this day the Jack Russell is thankfully still going strong as is my permission on the farm! .

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