A serious question: Why is this not a poem?

some would say use of a poetic device (effective or not) is enough in itself.  in this case, line breaks and the approximation of haiku form is poetic device.  hence, from that perspective, this is a bad poem, not a non-poem.  Good poems can also be written without a particular message - strong implications of mood can be enough to classify a piece of writing as poetic.

So, why is this not a poem? Victor Shklovsky distinguishes between poetic use of language and prosaic use of language - meaning prosaic relies on efficiency of understanding toward abstract concepts, whereas poetic impedes simple understanding and brings the reader to a fresh perspective of the moment and what's happening within that moment.  It wakes the reader up to experience, as opposed to the abstract idea of experience related in an historic fashion.  But he also focuses on device.  In the case of your cow, the device is only a facade.  There's no real poetic use of language, only a masquerade of broken lines and a cow munching on grass.