weird, I could swear I just posted a message here.. ok here it goes again:
The spores are not to be eaten by the cows, they should be on the air (naturally) or you can put in the dung directly.
psilocybe mushrooms can grow in a variety of substrates, including horse dung, but this is much more rare. They generally preffer the nutrients found in cow dung.
the thing is, in a natural environment, there are loads of other competing fungus. thats why when picking shrooms, you will walk around and look at many dungs which do not have any shrooms or have other non-active shrooms, and just a few will have the right ones. So if you get some spore syringes or spore prints and make the syringe yourself, and inoculate many different dungs, only few of them will eventually grow. But it is possible you start and then after that they will start successfully being ´regulars´ at your farm, spreading their spores and continuing automatically.
Another thing to notice is that inoculating cow dung with shrooms will only work if where you live has an appropriate climate for the shroom. for the usual psilocybe mushrooms, a humid and hot place is necessary. You could eventually water the dung yourself, if there´s not enough rain or humidity, but you couldnt do anything if its just too cold. Also if its too sunny, it might kill them. They generally like hot but indirect sun (so when picking shrooms many of them are sort of hidden in little mounts of higher grass that surrounds some dung).
so thats it, you gotta see if where your intended farm is, has the appropriate climate. If it does, are you sure it doesnt already have shrooms?