This depends on how you define and measure complexity. Information
processing is a different matter. Cows can't cope conceptually, and humans
can. Since conceptual coping is much more powerful than mere PERceptual
coping, we are functionally more complex than cows, by vast amounts. That's
why I can program a computer, write a book, drive a car, FIX a car, use the
Internet, dispute points of science and philosophy with other people, and so
on, while cows, even if they had human-like hands, would still be basically
not much more than grass-munchers.