Transgenic cows making modified milk
In 2000, AgResearch generated their first transgenic cows. These cows produced modified or ‘designer’ milk.
AgResearch received approval in 2010 to extend its transgenic cow research. Multiple generations of cows with the transgenic casein lines have been produced at the crown research institute's Waikato containment facility. In its 2018 report to the EPA, AgResearch noted that it had 12 transgenic casein cows, with the oldest born in 2003.
Cows with modified milk
AgResearch’s first transgenic cows had extra bovine (cow) kappa casein genes inserted in their genome. This resulted in increased kappa casein in their milk as the transgenic cow had their 2 naturally occurring kappa casein genes along with the inserted kappa casein gene(s).
Composition of cow’s milk
A table showing the components in cow’s milk. The exact composition will vary between cows and between different cow breeds.
This research was the first proof that transgenic technology could be used to modify milk composition in cows. Previous research by other groups overseas had focused on using transgenic cows to produce therapeutic proteins.
Casein is a key milk protein
Cow’s milk is made up of water, sugar, fat, proteins, vitamins and minerals. Casein makes up about 80% of the total protein in milk. It is one of the most valuable components of milk because of its nutritional value and processing properties. Casein is particularly important in cheese making.
Casein’s special structure
Casein proteins come in 4 different variants: alpha-s1, alpha-s2, beta and kappa casein. Each variant has its own amino acid composition, genetic variations and functional properties. These 4 casein variants combine to form a structure called a micelle. Micelles are dispersed in the water phase of milk and give milk its white colour.
Casein micelles.
Scientists propose that casein micelles consist of a complex of submicelles. The calcium phosphate and hydrophobic interactions between submicelles contribute to the stability of the micelle. Kappa casein around the outside stabilises the micelles against aggregation.
Key A: submicelle B: protruding chain C: calcium phosphate D: kappa casein E: phosphate group
Cheese is made from casein
The percentage of total casein in milk determines the cheese yield. Increased kappa and beta casein levels in milk are associated with improved heat stability, better cheese making properties and higher calcium content. Therefore, the more casein in the milk (particularly the kappa and beta forms), the higher its value.
Transgenic cows with extra casein
The milk from casein transgenic cows contained double the levels of kappa casein than milk from control cows. The milk from the transgenic cows had a slightly yellowish tinge when compared with normal milk. This is because the casein micelles in the milk are smaller, which affects the milk’s light scattering properties.
Transgenic cows with modified milk
Transgenic cows that over-express one form of casein (kappa) have the potential to provide economic benefits for cheese makers. Kappa casein decreases the size of the protein particles in milk, and this increases cheese yield.
Questions to consider What are the advantages of making casein-enriched milk? Did the expression of the transgene affect the milk composition or protein composition? Is there a visual difference between normal milk and casein-enriched milk? Why might this be?
Uses of modified milk
This research proved to the scientists that transgenic technologies could be used to alter milk composition in cows. In the future, modified milk from transgenic cows could be used to:
benefit animal health, for example, by improving growth and survival of calves
prevent animal diseases, such as mastitis
make milk with human health benefits
assist milk processing into dairy products.
Future of modified milk
Milk or meat products from transgenic animals are not allowed to enter the animal or human food supply in this country. New Zealand consumers are wary of the use of transgenic technologies in either animals or plants for food production, though they tend to be more accepting of these technologies when they produce therapeutic proteins for treatment of disease. It is important for New Zealanders to engage in the discussion about transgenic technologies and their uses, while considering ethical concerns and the potential impacts on animal welfare, food safety, labelling and regulations.
Useful links
Read about Dr Goetz Laible and the AgResearch team's success in knocking down beta-lactoglobulin (BLG), which forms a large part of the allergic reactions two to three per cent of infants have to cow's milk, in this 2017 New Zealand Herald article .
The AgResearch team were finalists in the 2013 KuDos Science Excellence Awards. This video highlights their work.
Read this news article, NZ team creates high protein GM milk , from January 2003 about AgResearch’s transgenic cows producing extra casein. The article was written by Graeme O’Neill and published on the Australian Life Scientist website.
This Ministry for the Environment booklet, Genetic Modification – The New Zealand Approach , published in 2004, aims to answer some of the basic questions you might have about what genetic modification is, how applications to use it can be made and how they are controlled and managed in New Zealand.
Read this 2019 report, Gene Editing – Legal and Regulatory Implications from the Royal Society of New Zealand.
