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?

DR GOETZ LAIBLE Casein is one of the major milk proteins, and casein is about 80% of all the protein in the milk, so it’s a highly valuable protein.

So what is the idea behind the casein transgenic cows? We had undertaken this study for different reasons, really. First of all, we wanted to try to increase the total amount of casein that is produced in milk and then also because the protein fraction in the milk has a lot to do with the functional properties of the milk when milk is processed into dairy foods.

So what we’ve found is that, by introducing additional casein genes, we have not been able to increase the total output of protein – so there’s a biological ceiling within these animals that regulates what is possible for them to produce – but we have been very successful in changing the composition of the different proteins. So for example, one of the proteins that we over-expressed was kappa casein – we found about threefold higher levels in our transgenic cows, compared to conventional or normal cows. And because the total amount of the protein doesn’t change, that means that we have seen a reduction of other milk proteins.

So there is quite a difference in the milk composition – in the protein composition – in its downstream effects on the processing qualities of the milk. The high level of kappa casein has been shown that it has an effect on decreasing the size of protein particles in milk, and that’s a major driver in the cheese making – the smaller the particles, the higher the cheese yield is – and so the basic idea should lead to higher cheese yields in cheese manufacture.

Acknowledgement: Christian Paul 123RF Limited