NZ team creates high-protein GM milk

New Zealand geneticists have laid the foundation for a revolution in dairying by developing transgenic dairy cows that yield high-protein milk.

Dr Goetz Laible's team at AgResearch's Ruakura Research Centre in Hamilton announced today in the online edition of Nature Biotechnology that it has selected two transgenic lines of Friesian cows whose milk contains up to double the normal level of kappa casein, and up to 20 per cent more beta casein.

The increases, which equates to an overall increase of 13 per cent in total protein content, could deliver higher profits for dairy farmers, while cheesemakers should benefit from the milk's enhanced processing qualities.

Laible's team inserted extra copies of the beta and kappa casein genes into fibroblast cells from the lung tissue of a female calf foetus, from a cross between an elite, progeny-tested Friesian bull and Friesian cow selected for exceptional milk yield.

Milk casein consists of a complex of four different proteins: alpha caseins 1 and 2, beta casein and kappa casein. They form a colloidal complex of microscopic, bubble-like micelles.

The New Zealand researchers transfected the fibroblast cells with extra copies of the beta and kappa casein genes.

Beta casein is a major calcium-binding protein in milk, although Laible’s team has not detected any increase in the calcium content of the transgenic cows' milk.

But potentially more important is the doubling of the level of kappa casein, the protein that encapsulates the casein micelles.

By grafting on the promoter, or regulatory element, from the beta-casen gene, they were able to double the output from the kappa casein gene.

The team believes the higher ratio of kappa casein in the casein, which results in smaller micelles, should improve the heat stability of the milk and improve its cheesemaking properties -- it may decrease the time taken to coagulate the curd using the clotting agent chymosin (rennet), and improve whey expulsion.

High success rate

Laible's team produced 11 transgenic calves, representing four different donor cell lines, by fusing the transgenic fibroblasts with enucleated oocytes. From the resulting calves they selected two lines producing the highest protein levels in their milk.

Laible said milk normally contained about 5 per cent protein; in milk from the best of the transgenic cows, protein content is around 5.65 per cent.

Since bulk milk prices are based on protein content, the protein-enriched milk would increase returns to dairy farmers by around 13 per cent, with a corresponding increase in yield and efficiency for cheesemakers.

Laible said the transgenic cows would be used for further research predicted benefits of increased kappa casein on cheesemaking have yet to be confirmed.

He said it would be a major undertaking to transfer the benefits to New Zealand's dairy industry -– in the paper the team suggests that assisted reproduction technology could be used to breed a bull carrying a double complement of the two genes, which could then be cloned to accelerate the introduction of the new trait into commercial dairy herds.

Until now, most efforts to genetically engineer cattle or sheep milk have been directed at using the udder as a convenient, high-volume expression system for very valuable therapeutic proteins; the New Zealand team is the first to produce animals in which the protein content and protein balance of the milk has been modified for potential commercial advantage.

According to their Nature Biotechnology paper, the results "show that it is feasible to substantially alter a major component of milk in high-producing dairy cows by a transgenic approach and thus to improve the functional properties of dairy milk."

The transgenic Friesians would give New Zealand cheese and dairy products a substantial pricing advantage in export markets if it kept the technology to itself.

New Zealand's current political climate -- including opposition from the Greens and other groups opposed to the use of genetically modified organisms (GMOs) in New Zealand agriculture -- could be an obstacle to commercialisation. There is currently a moratorium on agricultural GMOs in New Zealand.

Meanwhile Australia's Cooperative Research Centre for Innovative Dairy Products is already working on similar research to develop 'designer' dairy cattle with modified milk.