The breakthrough - hailed as internationally "seminal" - had been kept under wraps by AgResearch until this morning and will be published in the prestigious American science journal Proceedings of the National Academy of Sciences.
The AgResearch team, led by Dr Goetz Laible, wanted to discover if they could produce milk which contained less of a particular milk protein known to be allergenic.
"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," said Dr Stefan Wagner, one of the lead authors on the paper.
"Two to three per cent of infants are allergic to cow's milk, and BLG allergies make up a large part of that percentage."
The scientists first tested the process in a mouse model engineered to produce the sheep form of BLG protein in mouse milk.
Employing a technique called RNA interference, two microRNAs (short ribonucleic acid molecules) were then introduced into the mouse to knock-down the expression of the sheep BLG protein, resulting in a 96 per cent reduction in the sheep BLG protein in mouse milk.
They next produced Daisy, a female calf genetically engineered to express the same two micro RNAs, this time to target the BLG protein that is also a normal constituent in cow's milk.
They then hormonally induced Daisy to lactate.
The resulting milk collected from Daisy had no detectable BLG protein and, unexpectedly, also had more than twice the level of the casein proteins that also normally occur in cow's milk.
"People have long looked into reducing this enigmatic protein, or completely knocking it out, because there has been no definitive function able to be assigned to it," Dr Wagner said.
"So, we developed this scientific model to investigate the effect of knocking BLG protein out on the composition and functional properties of milk, and to determine whether the absence of BLG produces cow's milk that is hypo-allergenic."
Dr Wagner described this as the project's "real discovery component" - and Daisy, now 11 months old, gave the team many answers.
"To avoid the delay of two years before a natural lactation, the milk we analysed was from an induced lactation," he said.
"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."
In the future, the basic process of using designer microRNAs to target other genes could provide an efficient tool to change additional livestock traits, such as producing animals with enhanced disease resistance or improved lactation performance, he said.
Malaghan Institute research director Professor Graham le Gros praised the discovery.
"This outstanding breakthrough has enormous implications due to its potential to reduce the significant impact milk allergies have on our children and neatly avoids the concerns associated with genetic modification of the milk proteins themselves."
AgResearch was reluctant to go into the project's commercial potential, saying that development was restricted by tight regulations around genetic modification.
- Jamie Morton, New Zealand Herald
