New Zealand researchers have genetically engineered a cow to produce milk free of the protein that causes allergies in children.

The milk could also prove to be healthier than normal milk as it contains higher levels of the protein casein, which would result in higher calcium levels and improved cheese yields from the milk.

The development targets the two per cent to three per cent of infants in the developed world who are allergic to cows' milk proteins — used in the production of baby formulas — in the first year of life.

The researchers add that the success of their approach suggests it may also be used to alter other traits in livestock.

The development, published this week in Proceedings of the National Academy of Sciences, uses a technique known as RNA interference to block the production of the protein, beta-lactoglobulin (BLG).

Co-author Dr. Stefan Wagner, of AgResearch in New Zealand says BLG is produced in cows and other ruminants, but is not found in human milk.

He says although it has long been suspected as a milk allergen its remains "enigmatic" and its role in cows' milk is unknown. The study he says was based on a "very simple idea — to completely knock [BLG] out."

To do this the team had to first develop a "designer microRNA" (short ribonucleic acid molecules) to target the BLG protein, he says. They then developed a mouse model that could produce milk containing BLG and introduced into the mouse their designer microRNA to knock-down the expression of the BLG protein.

This initial work, says Wagner, led to a 96 per cent reduction in BLG.

Cloning a calf

The team then turned its attention toward cloning a calf with the same anti-BLG trait by transferring 57 cloned embryos into cows.

This resulted in five pregnancies with one live female calf, known as Daisy, born without a tail — a defect the researchers say is linked to the cloning rather than the omission of BLG.

The team then hormonally induced Daisy to lactate and analysis of the milk "to our surprise," says Wagner, shows no detectable levels of BLG.

Wagner says Daisy was induced to lactate "to avoid the delay of two years before a natural lactation."

"We only obtained small quantities over a few days for these initial studies. We now want to breed from Daisy and determine the milk composition and yield from a natural lactation. We also want to investigate the origin of Daisy's 'taillessness,' a rare congenital disease in cows."

Commercial use a long way off

Wagner says the absence of BLG has a strong effect on the composition of the milk, with greatly enhanced levels of other milk proteins, in particular casein. The higher levels of casein correlate with increased levels of calcium and improved cheese yields from the milk.

In the future, the authors suggest, the methods could potentially serve as an efficient tool to target additional genes and modify other livestock traits such as enhanced disease resistance or improved lactation performance.

Wagner says the researchers expect the work to raise criticism from anti-GM groups, but it remains tightly regulated. The animals were being kept in containment systems and the milk is only used for analytical purposes.

He says any commercial use of the milk is a long way off as the research must now wait on analysis of milk from natural lactation by Daisy.