The worldwide scientific first has led to a genetically engineered cow called Daisy.

Milk is natural and full of calcium, but for hundreds of thousands of children milk causes severe allergic reactions.

Milk allergy is the second most common form of food allergy - behind eggs.

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As a newborn two-year-old Indigo Yamaguchi started developing a rash every time her mother Edwina breastfed her.

"It kept getting worse and worse, and by about three months it was bright red and pussy, and she could not stop scratching. It started coming down her arms and legs, and she'd be up six times a night. It was hell when I look back on it," Edwina said.

After much misdiagnosis, Dr Elizabeth Pickford suggested Indigo may be allergic to the cows' milk her mother was consuming.

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"I stopped eating milk, cheese, eggs and anything with dairy, and within a week all her rash was gone," Edwina said.

According to Dr Pickford, the reason allergy to milk develops as a baby is that "there are many different types of proteins in it, and sometimes what happens is the person's body will recognise one of those particular proteins and then attack it. It doesn't appear for any good reason, but just for some reason it looks at it and says 'that looks nasty, I think I'll get rid of it'."

Most kids grow out of it by age three, but for some it remains - but finally there is hope, in a paddock in New Zealand.

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Goetz Laible is the senior scientist at AgResearch in New Zealand - a national Government research group that's won the race against scientists worldwide to genetically engineer a cow that produces milk without BLG - one of the six key proteins that cause severe allergies.

"BLG is certainly a major one. Removing it is a big step forward to removing some of the issues," Laible said.

Daisy the wonder cow is completely unaware of her unique ability, but the scientists who created her believe she is the key to helping millions of milk allergy sufferers around the world.

This reporter is on Twitter at @LauraSparkes7