Always amazing, but does anyone else have a problem with the very basic premise?

Rating: Null/10 (25 November 2008)

My problem:
Amazing as this series is, and relevant on many levels, I have a problem with the entire basic premise: If the machines subjugated humanity purely as batteries, why didn't they use a more docile animal source? Surely Cows make more energy and heat per individual than humans, and they wouldn't have had all the problems of people 'thinking' and wanting to break out of control.
The reason for the Matrix is to entertain the minds of the humans as they were used for energy. But if they had used cows, all they'd need is a picture of a grassy field and plenty of milk and grass, problem solved.
Does anyone else have an issue with the premise of this entire daydream?
If an epic story is to be so well developed, and have such intensity of script and action, can't we now go back and fix the few flaws from the outset, such as at least make the machines complex enough to be choosing humans as revenge, justifying their use over other more docile beasts to power the machines?