Cloned cow gives 'allergy-free' milk

Ian Sample
Researchers have created Daisy the cow with the same procedure used to make Dolly the sheep.

A genetically modified cow whose milk lacks a substance that causes allergic reactions in people has been created by scientists in New Zealand.

In their first year of life, two or three in every 100 infants are allergic to a whey protein in milk called beta-lactoglobulin (BLG) . The researchers used a cloning procedure to engineer the cow, called Daisy, to produce milk that does not contain the protein.

The genetic alteration slashed levels of BLG protein in the cow's milk to undetectable levels, but it more than doubled the concentrations of other milk proteins called caseins.

Scientist Stefan Wagner said they now planned to investigate whether or not the BLG-free milk caused allergic reactions. "First of all, we will have to determine whether the lack of detectable levels of BLG will impact on milk yield."

To make Daisy, scientists used the same cloning procedure that created Dolly the sheep in 1996. They took a cow skin cell and genetically modified it to produce molecules that block the manufacture of BLG. The nucleus of this cell was then transferred to a cow egg that had had its own nucleus removed. This reconstituted egg was grown in the lab until it formed what is called a blastocyst (a ball of about 100 cells) and then transplanted into the womb of a foster cow.  

The cloning technique is not completely efficient. Of about 100 blastocysts the scientists implanted into cows, more than half of the pregnancies failed early on, and only one live calf, Daisy, was born.

Bruce Whitelaw, professor of animal biotechnology at the Roslin Institute at Edinburgh University in Scotland, said the major advance was demonstrating that the genetic procedure, called RNA interference, works in large animals. "Many people have been talking about using this technique to better arm an animal to combat a virus infection and this adds momentum to that work."

Last year, the Roslin Institute used a related technique to create chickens that cannot spread avian flu.

The New Zealand team is also working on why Daisy was born without a tail. The cloning process, rather than the extra genes she carried, is most likely to blame for the birth defect. – ©Guardian News & Media 2012

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