Doug Dibley, demonstration manager of Owl Farm at St Peter's School in Cambridge says it would be very difficult to run a modern dairy farm if cows and calves were kept together.

The New Zealand dairy industry would cease to exist if farmers halted the removal of bobby calves from cows.

Dairying experts say keeping calves on their mothers would be massively impractical and cause animal welfare issues.

Animal rights activists from Farmwatch and SAFE claimed that removing calves from cows soon after they were born highlighted the cruelty of the dairy industry, during Sunday's expose which showed hidden camera footage of bobby calves being mistreated by farmers, stock truck operators and slaughterhouse workers.

The only way to justify separation anxiety felt by a cow when its calf was removed was to look after calves as best as possible, Massey University Professor of animal welfare science David Mellor says.

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However, dairy farmer and Lincoln University farm management lecturer Marvin Pangborn said removing calves from cows was a basic element of dairy farming.

"We can move away from that if they want us to, but there would be no dairy industry."

Pangborn said removing calves was mainstream dairy farming practise in the modern world and was carried out in most dairy industries in the northern hemisphere.

Keeping calves with their mothers would create massive logistical issues for farmers during twice daily milking.

"In fact that would be as big an animal welfare issue - bringing a lot of calves in with a yard full of cows."

The economics of leaving calves with cows were also "horrible". Calves would drink milk produced by cows, leaving less to be sold and decreasing farm profitability, and milk fever would likely increase.

"The thought of a dairy industry where you didn't take the calves away, it evokes images of the third world where people milk two cows and the cow is on one side and the calf is on the other. That's not what normal industrialised dairying is about."

Pangborn said he accepted how the practise of separating calves from cows might be perceived by people, but if it was stopped, it would effectively mean the end of the dairy industry.

"If we quit producing milk, not only does it take away one of the leading nutritional aspects to the human diet, it also destroys the New Zealand economy."

Animal rights activists could not have it both ways. If calf separation was banned, saved calves would be unable to be kept on a farm because it would be uneconomical, Pangborn said.

Owl Farm demonstration manager Doug Dibley✓,at St Peter's School in Cambridge, said it would be difficult to run a modern dairy farm if cows and calves were kept together.

A cow would have to be separated from its calf, walked to the milking shed with the rest of the herd, milked so it retained enough milk for its calf and then returned to the paddock and matched with its calf.

It would also cause animal health issues including milk fever and mastitis. Dibley said his staff followed best practise guidelines for removing a calf from its cow. A trailer lined with rubber matting and shavings and towed by a quad bike was used to pick a calf up to be transported to the farm's calf pens.

Both bobby and heifer replacement calves were placed in a warm and dry environment in the farm's rearing facility. The animal's naval was sprayed with iodine to reduce the chance of infection and it was fed two litres of colostrum twice a day.

"You make sure, even though it's a short lifespan, [that it has] a good quality of life."

Cows had been developed to produce large amounts of milk that was impossible for their calves to consume, said Massey University animal welfare science professor David Mellor.

"We have to make sure the harms are absolutely as low we can make them and the benefits are as high as we can make them."

That included how well calves were looked after being separated.

"Yes there is separation anxiety, but the only way we can justify that is if we do everything else really, really well to minimise what the mother might be feeling."

Calves did not feel this anxiety so long as they were well managed and well fed, he said.

Mellor said the industry was dealing with babies. Humans were genetically designed to protect and nurture vulnerable young and this explained their strong response to footage obtained by SAFE, including the scenes of a cow running after its calf when it was taken away, he said.

"That is what is being reference by that programme and by SAFE when they say, 'this is cruel'."

There were few alternatives for the industry. One that did exist was injecting the cow with oestrogenic, androgenic or progestagenic hormones that caused a cow to produce milk but not a calf.

Pangborn said this was a "nightmare" from a farming perspective. He worked on a farm that used this practise 15 years ago occasionally on its cows. Multiple injections and massaging the udder were required to induce the milk.

"You couldn't do that with 500 cows."

The New Zealand Veterinary Association also did not support hormone use. Hormones were considered a risk to animal welfare and ran contrary to conditions of trade imposed by several of New Zealand's major trading partners.

Other options included dairy farmers using sexed semen so a cow only produced a heifer calf or using emerging science to "edit" a cow's genes so it produced only female offspring.