Milk from cows contains a protein known as β-lactoglobulin, (BLG) which is a major human allergen. This GMO is a cow that contains genes from a mouse.
How it was Created
This GMO was created by a team of researchers led by R. Martinus. It was made because BLG, found in cow milk, is a major human allergen. By making BLG - free milk, many humans allergic to BLG could drink milk again. The GMO was made by taking a BLG expressing gene from a mouse and putting into a cow. The resulting GMO cow produces milk that is allergen free.
Pros and Cons
Pros: Humans can drink the milk without an allergic reaction, there is no harm to the cows, and the milk is tastes exactly the same.
Cons: Long term effects could be dangerous, people might now want to drink GMO milk, and GMO cows might be too expensive for the average farmer to buy.
I believe that a lot of GMOs, including this one are good and should be used. This would allow people who can't drink milk to actually be able to drink it. People could buy GMO milk and not have to spend extra money on things like soy milk.