Hardware disease is caused by cows ingesting metal fragments which they may have accidentally swallowed while grazing. Photo: RNZ / Susan Murray
Dairy farmers are being warned about the dangers of their cows eating metal which can kill them - and some farmers are using magnets to detect the fragments.
Metal can come from machinery on farms, fencing wire or broken equipment. A decade ago the Ministry for Primary Industries cracked down on metal in imported feed such as palm kernel extract by requiring importers to screen it for foreign objects before supplying it to farms.
Some dairy farmers are using a magnetic strip for their feed mixers to prevent hardware disease that's caused by the metal fragments and kills cattle.
Another option is inserting a medical magnet into cows guts - that looks like a large gel covered pill that stays in their stomach for life - and any metal debris or wire they may have swallowed while grazing attaches to it - preventing fatal damage to their intestines and heart.
Ashburton dairy farmer Craig Hickman milks just under a thousand cows and said he purchased a magnetic device so that any metal particles, wire or nails stuck to it at the bottom of his feed facility.
Hickman said initially he was not very interested as it costs $2500 - but agreed to a trial.
"So we struck a compromise where I could install it and test it for a month. If I caught any bits of metal I would buy it and if not they would come and take it back out and wouldn't charge me anything."
Hickman said after three days - or six milkings - he checked it and found a fairly long slither of sharp steel that could perforate a cow's gut.
"Every year you get a cow or two that will get sick - go off colour and skinny and waste away. You either pet food them, cull or euthanise them or they will die. It could very well be hardware disease."
A dairy cow is worth about $1500 and Hickman said installing a magnet was money well spent.
"It wasn't a problem I wasn't aware of but we've got a solution for it now. Once you see those bits of steel that have been coming through I would have hated to think of any cows eating those - so it's great peace of mind."
Hickman said he had also found metal fragments from locally bought hay, wheat and silage, as well as Palm Kernel feed, stuck to his magnet.
It was unusual to get metal in imported feed here, he said, but in some off-shore countries such as the UK and North America many farmers put a cigar shaped magnet in every young cow's gut to prevent her dying from hardware disease.
A vet from the Rangiora Vet centre uses these - and said cattle did not chew their food much before swallowing it so it was not difficult for them to swallow a foreign object. They can also lick metal filings up from milking shed floors.
Andrew Weir said it was difficult to tell if the cow was unwell due to metal in their intestine without an expensive autopsy - but if a cow was sick and he had not been able to confirm why - he sometimes put a small medical magnet down their throat and into their gut.
Internal magnets help prevent hardware disease by attracting stray metal cows have eaten from the folds and crevices of the intestine before they can pierce the gut lining.
"From time to time we come across cows that are non-specific sick with nothing obvious going on and some of those cows are doing that because of hardware disease when they have eaten some metal. They will just get sicker and sicker and die."
He said magnets were a lot cheaper than a cow and if there was an issue with metal in a specific cow, or property, then it was a much better option than losing cows.
However Weir said putting magnets into a cow's gut would not work if the metal had already drilled its way towards their heart - and then caused a fatal infection.
The Ministry for Primary Industries said there were strict import health standards for products, including palm kernel extract from Indonesia and Malaysia.
All feed must be screened on arrival using a mesh no greater than 4mm in size to remove any physical contaminants and doing this was the responsibility of feed importers, it said.
MPI said it also audited palm kernel supply chains and they were currently meeting biosecurity requirements.
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