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Transgenic cows making modified milk

In 2000, AgResearch generated their first transgenic cows. These cows produced modified or ‘designer’ milk. Discover why the scientists did this research and what they found.

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).

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 .

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.

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 here or overseas. 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.


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