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 hundred infants are allergic to a whey protein in milk called BLG. The researchers engineered the cow, called Daisy, to produce milk that doesn't contain the protein. While the genetic alteration slashed levels of BLG protein in the cow's milk to undetectable levels, it more than doubled the concentrations of other milk proteins called caseins. The cow was created with the same cloning procedure that led to Dolly the sheep in 1996. Most of the differences between cow and human milk do not cause problems for people who consume it, but BLG or beta-lactoglobulin protein, which is found in milk from cows and other ruminants, is a major cause of allergic reactions. To make Daisy, scientists took a cow skin cell and genetically modified it to produce molecules that block the manufacture of BLG protein. The nucleus of this cell was then transferred into a cow egg that had its own nucleus removed. The reconstituted egg was grown in the lab until it formed what is called a blastocyst, a ball of around 100 cells, and then transplanted into the womb of a foster cow. The cloning technique is not efficient. Of around 100 blastocysts the scientists implanted into cows, more than half of the pregnancies failed early on, and only one live calf, Daisy, was born. One question the New Zealand team is working on now is why Daisy was born without a tail. The cloning process is most likely to blame for the birth defect.