Riddled in story

30 cows in a field, 20 ate (28) chickens, the answers 'Ten' if you knew how many didn't. Apparently they were carnivorous cows,
Feeding off on human flesh, to compensate the chickens that fled
The first victim was the farmer, he wasn't with a armor
He got butchered and cooked into stew
The cows hate grew, drinking blood-the toxic brew

Replacing their hunger for chicken to human meat, they slaughter the farmers lone son, now there was no one to mourn
An alarmed neighbor called the police, only one dispatched to the scene
Unaware of the murderous presence, she thought it was only a dream
Until her head and body split, an axe did the trick, floor blood red previously creme'
The old hag didn't see it coming...

Now the officers fate is tied as he appears late at the scene
He sees a cow beside the breathless body, nothing suspicious about the animal
As the cop investigates, the animal comes closer-it is hannibal!
Unwary of it's murderous intent, he got his body hacked, organs disemboweled

Now laying in a pool of blood, slowly his life is fading...he succeeds to warn the precinct.

Five more officers arrive at the scene None knew what was coming
The end was near as the cows were seen
Unaware of the slaughtering cows, no signs of danger
Caught by the horde of cows, the world grew stranger
Four of them slain to fulfill the cows hunger

One got all of his limbs torn apart
Another got his chest punctured
One was burnt alive
Another got severely tortured, till he was no more aware, got his brains out of the cranial sphere
One survived witnessing the madness and that's me, no rhyme here
Although survival comes with a price, mind engraved in maddening fear

And hence a small story has come to a gory conclusion, so don't undermine the question i.e There are 30 cows in a field, 28 chickens. How many didn't?
Can't solve the riddle? The answer's given!