Cows can trace their ancestry back several millennia...to about eighty cows in the area of what is now Turkey. This means that the cows we know (and eat) today are merely the result of a careful breeding program that took place eons ago to create the perfect, genetically engineered cow.
They have been genetically engineered to produce healthier milk. Scientists have created cows that have been genetically modified to produce milk which is healthier for humans. The cows are part of a growing effort by scientists to make food and drink products from livestock healthier by genetically altering the animals.
Yes, cows are genetically engineered, because they have been bred selectively for years. Farming can become more efficient and cattle can become stronger through this engineering. It is wise for farmers to produce a good crop. That is the essence of good farming. Through generations, cows have produced more milk, and produced more and better meat.
Cows haven't changed in appearance much but I do think they have gotten bigger. This does not mean they are genetically engineered. They maybe genetically modified in some cases but that's not the same as saying that a cow was engineering in a lab from a goat and a horse.