Stray voltage can create milking-time mayhem, but producers should rule out other factors before blaming electrical issues for unusual cow behaviour. We spoke to two specialists to find out more.
TEXT RACHAEL PORTER
Not all surprises are ‘nice’ and unexpected shocks can certainly put cows literally off their milking stride. But is stray voltage really a common issue on UK units and something producers should keep in mind?
“No, it’s quite unusual, but that’s not to say it’s not causing problems on some units,” says the Milking Equipment Association’s technical specialist John Baines. “But in 99% of cases where producers think there is an issue with stray voltage, it’s typically something else. He adds that when there are problems or changes to cow behaviour in the milking parlour, many producers are looking for one thing to blame.
But there can be multiple issues, like delayed milk let-down, incomplete milking out, fidgeting, and excessive dunging and urinating. These can all be signs of stray voltage. “But don’t assume this, they can also, for example, be due to lack of stimulation or poor teat skin condition. Pre and post teat dipping isn’t just about hygiene – it’s also about moisturising teats. Skin condition can quickly deteriorate in cold and dry conditions. Flies can also be a major irritant, and cows that are too large for parlour stalling may not be able to stand correctly, resulting in fidgeting. All can contribute to an ‘uncomfortable’ milking experience.”
And Mr Baines reminds producers that milking routine can also play a role, as can liner choice. Swelling around the base of teats can be due to periods of low/no flow from the teat. If this is caused by lack of preparation, it can result in incomplete milking. “So check the milking machinery, pulsation, liners, cluster alignment, and the milking routine itself. On most units any one of these could be the culprit, or indeed the culprits.”
That said, electricity can occasionally be the problem. “But I always urge producers to exhaust all the other options first, through a process of elimination, and not least because getting to the bottom of a stray voltage issue can be tricky, time consuming and expensive. So rule everything else out first.
Where stray voltage is an issue, Mr Baines says it’s either due to poor earthing or wiring installation. “The neutral to earth differential is key here. Ideally this should be near to zero, but it can occasionally higher. This isn’t a safety issue or something people could detect – particularly when wearing rubber boots in the parlour, but cattle are much more sensitive to stray voltage. Just half a volt across a cow’s contact points – her nose and her rear end – can be enough to change her behaviour. “Cows have wet feet, noses and teats and they are also larger and longer than a person, so there’s a long way to ‘bridge the gap’ between two points and feel a shock. Certainly more easily than we would do.”
Ian Ohnstad: stray voltage is often blamed if cows are underperforming
The Dairy Group consultant and milking technology specialist Ian Ohnstad agrees that stray voltage is rarely an issue when it comes to abnormal milking behaviour, although it’s often blamed when cows are unsettled in the parlour – or underperforming. “It’s a little like when you go to your GP because you’re feeling unwell, with a myriad of symptoms. They’ll often put it down to stress because it’s a good ‘catch all’.
Rule out
“But, it’s good to get to the root of any problem, and this should start with investigating and ruling out other possible causes.”
Mr Ohnstad says, in his experience and particularly during the past 10 to 15 years, stray voltage is rarely an issue. “It’s not something we see often, mainly due to how new parlours are installed.”
He says there are exceptions, but these are usually the result of an unusual or catastrophic event. “One example was a tractor loader that drove onto a yard and brought down the main power cable. Every piece of metal work on that yard became live. But luckily no people or livestock were hurt.”
Mr Baines says that stray-voltage issues are, when they occur, obvious. “Cows will actually refuse to come into the parlour – it’s like there’s an invisible fence in front of them. Or the converse can be true – they’ll leave the parlour like a greyhound from a trap.
“I remember a client who had cows go down in the collecting yard, and there was an employee in the parlour in hobnail boots and sparks flew. That was also an obvious and easy problem to spot.” In that instance, there was a problem with the wiring in the old cottages situated close to the parlour.
Mr Ohnstad agrees that stray voltage in and around the parlour is rarely subtle. “Cows will be extremely reluctant to enter and will bunch up in the collecting yard. If they do enter the parlour it will be tentative – they’ll look ‘awkward’. You may notice them avoiding touching any metal work – such as troughs and rails – with their wet noses. They’ll be hunched up.
He says ‘stray’ is probably the incorrect term to use for the voltage. “It should be voltage differential. That’s what the cow is potentially picking up when she touches metal work – she acts like a conductor and the amps pass through her.”
Faraday cage
Today’s parlours are designed and built with this in mind, and metalwork is earth bonded. In the past, copper bands were put around the base of feeders and posts to link them to the steel RSJs, to also earth metalwork. “But these are less than ideal as the cows are ‘interested’ in them – they like to lick the copper – and it can become damaged. They’re not robust enough for the cow environment. “So new installations are based on the Faraday cage design. Metalwork is welded to RSJs that are, in turn properly earthed. Any parlour designer, fitter and dairy electrician knows how important it is to earth parlours. Metal, water, livestock and electricity don’t go well together.
"But do remain observant. Little things can do wrong. I visited a herd a few years ago where the cows in the parlour visibly flinched every time the variable speed milk pump kicked in. It was clearly generating a voltage differential, and the cows were definitely reacting to it. Once spotted, it was relatively easy to fix.”
So it can and does happen, but it is highly unusual. “It’s rarely the wiring – rodent damage shouldn’t be an issue if the correct cabling with trips and fuses to protect the installation are used. But do keep an eye on this in older parlours. Most importantly, just watch your cows. They’ll soon tell you if there really is a problem.”
Stray voltage pointers
● Watch and observe your cows in the collecting yard and in the parlour for unusual or sudden changes to behaviour
● Eliminate other possible reasons for behavioural issues, such as poor teat condition or liner performance
● Always use a registered and fully-qualified/certified electrician, ideally with livestock/milking parlour experience.
● Ask for a full report on the power supply to your farm
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