I tried approaching an enchanted cow and it (he?) ran off... Admittedly I do not have a lot of experience with real cows, but I did not expect that. Maybe someone read this post to it and the cow did not want to stick around for the experiment.
You get an unintelligent animal who has been turned into a person, you better believe they are going to be spooked and will very much be likely to run off. They have no idea what is going on and will be running off of pure fear and panic. Whether they would produce milk or lay eggs depends on a number of factors, that would be too diverse to get into, especially with the possibility of magic changing the rules.