The following from    http://www.aurochs.org/cows/songs/

Hey Diddle Diddle
Hey diddle diddle, the cat and the fiddle,
The cow jumped over the moon,
The little dog laughed to see such fun
And the dish ran away with the spoon.

Old English Rune Poem
Each verse of the Old English Rune Poem begins with a letter of the Anglo-Saxon runic alphabet and describes what the rune stands for. The second verse (ur) concerns the aurochs:

Ur byþ anmod and oferhyrned
felafrecne deor feohteþ mid hornum
mære morstapa þæt is modig wuht

This translates as:

Aurochs is a courageous beast, having huge horns,
A savage beast, it fights with its horns,
A noble stalker of the moors, it is a fierce beast!

Tom Wulf provides the full text and English translation.

Purple Cow - by Gelett Burgess
I never saw a purple cow;
I never hope to see one;
but I can tell you anyhow;
I'd rather see than be one!

See Wikipedia for the history and context of this and the following poem.

Confession: and a Portrait Too, Upon a Background that I Rue - by Gelett Burgess
Ah, yes, I wrote the "Purple Cow".
I'm Sorry, now, I wrote it;
But I can tell you Anyhow
I'll Kill you if you Quote it!

The New Cow - by August Derleth
The new cow came through the gate,
And her calf came after, a little late.
No longer willing to be led,
The calf went on ahead,
While she stood to look around
Over the hills and lower ground
Stood shyly, defiantly there,
Smelling flower-fragrant air,
And gazed toward the old cows
Grouped on the way before.
Knowing not how she might stay
Among them, stranger still,
She hesitated yet, now they had turned
At the foot of the hill
And seemed to wait for her at the gate,
To wait for her who was strange and thin,
Til she came on,
And they opened their ranks
To take her in.

The Cow - by Robert Louis Stephenson
The friendly cow all red and white,
I love with all my heart:
She gives me cream with all her might,
To eat with apple-tart.

She wanders lowing here and there,
And yet she cannot stray,
All in the pleasant open air,
The pleasant light of day;

And blown by all the winds that pass
And wet with all the showers,
She walks among the meadow grass
And eats the meadow flowers.

the way to hump a cow is now - by e e cummings
the way to hump a cow is not
to get yourself a stool
but draw a line around the spot
and call it beautifool

to multiply because and why
dividing thens by nows
and adding and(i understand)
is hows to hump a cows

the way to hump a cow is not
to elevate your tool
but drop a penny in the slot
and bellow like a bool

to lay a wreath from ancient greath
on insulated brows
(while tossing boms at uncle toms
is hows to hump a cows

the way to hump a cow is not
to push and then to pull
but practicing the art of swot
to preach the golden rull

to vote for me(all decent mem
and wonens will allows
which if they don.t to hell with them)
is hows to hump a cows