Read a report on the affects of genetically engineered animals on the animals themselves, humans, and the environment.
foe.org
www.ncbi.nlm.nih.gov
I've personally been to one mass production farm (in the uk) through a lecture trip. We've been able to genetically engineer and mofidy animals and plants since the early 1980s.... heck we can even clone and make hybrids!
GMO is used mostly in food industries to enhance certain aspects of an organism which makes it more suitable for our needs (and cheaper).
These changes include; faster growth rate, larger growth capabilities, less muscle and fibres, more fats etc...
Im surprised youre not familiar with this. There was (still is) a huge argument over the ethics of GMO.