Just to clear up a bit of confusion - feeding the Cow Plant meant it wouldn't eat people. If you didn't feed it, it would produce a cake, which a sim would try to grab, and the Cow Plant would then eat them up, and produce a milk. The milk, when drunk, would act like Ambrosia - either reset the Sims' age, or take a few days off it (I can't remember which).
In the Sims 2, it didn't eat Pets, so I highly doubt EA would do it this time.
And also, I'm kind of apprehensive about this - I didn't play with the Cow Plant often, but I liked it when I did. Unfortunately, I've only got 75 SimPoints after getting my Simmies a bed.