Why the matrix "energy" humans instead of animals

It's most likely due to fact that humans would likely produce more bioelectricity than animals. While it may be around the same over most of the body when in comparing to animals, humans would likely still have a bit more from the brain and synaps firing due to thought process, etc. While it's likely the lowest biochemical reaction to cause bioelectricity, it'd still fire more when compared to animals who's thought process just boils down to basic instincts. Not to mention as well when speaking about storage space. Overall, humans will average out in size. You'd just need an average size containment unit(the egg things they were housed in before awakening) to handle humans. Something 8 - 10 feet tall in order to leave room for reflexive motion during dream state even for the really tall ones. For animals, presuming you're not just sticking with one type, you'd need a variety of sizes, thus boiling that down to a matter of convenience. Sience and logic aside, it just wouldn't make a great movie if "The One" was a puppy, kitten or even blue whale if you will.

u are right. i think humans will convince the machines to use animals for energy. but the animal rights activists might not like the idea and the plan might not move on. anyways the machines require energy and they get it from electricty or the robots get it from batteries so the humans can easily cut off their power unless the humans create the machines to work from solar energy.