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People allergic to milk products can now breathe a sigh of relief - a group of scientists have created a genetically engineered cow that yields hypoallergenic milk.

Scientists from New Zealand's AgResearch led by Goetz Laible, head of the transgenic livestock program, have created a transgenic cow producing milk with less protein called beta-lactoglobulin (BLG). Some humans, in particular, children are allergic to BLG.

The BLG is an important whey protein in cow, sheep and in breast milk. This particular protein can cause allergic reactions in some children feeding on cow's milk.

For their study, the research team tested their method on a mouse that is modeled to produce sheep form of BLG protein in mouse milk. They used a technique called RNA interference, where two microRNAs (short ribonucleic acid molecules) used to knock out the expression of BLG genes.

As a result, there was a 96 percent reduction in the sheep BLG protein in mouse milk. Then experts tested a female calf named Daisy, who was genetically engineered with the same RNA interference to reduce the BLG protein in cow's milk.

When they induced the hormones of Daisy to lactate, they found there was no detectable trace of the BLG protein. However, they noticed a twofold increase in the levels of casein proteins, that occur abundantly in cow's milk.

"We were successful in greatly reducing the amount of beta-lactoglobulin (BLG), a milk whey protein which is not in human breast milk and which can cause allergic reactions," Dr Stefan Wagner, one of the lead authors of the paper, said in a statement from AgResearch.

"Two to three percent of infants are allergic to cow's milk, and BLG allergies make up a large part of that percentage," he said.

While the new technique is considered as major breakthrough, experts note that they are planning to breed from Daisy and determine the implications of the RNA interference on the milk composition and milk yields from natural lactation.

The findings of the study, "Targeted microRNA expression in dairy cattle directs production of β-lactoglobulin-free, high-casein milk", are published in the journal of the Proceedings of the National Academy of Sciences.