Ive noticed that EIO spawners stop creating new mobs if theres already a few around unlike MFR spawners that will just continue spamming them til you have hundreds. Im not sure how it works, are those "special" EIO cows? Or does it simply read how many cows are within its radius? If you spawned the cows in the other pen with the spawner then you might need to go out and get some wild ones. Or maybe you just need to move the spawner away from them.