This is Robert Ernest Gilbert's (1953) "Thy Rocks and Rills".
An intelligent (talking) bull is spoiling for a bullfight.
Stonecypher concealed spear and dummy beneath the floor of the dog
house. Going to the paddock, he patted the bull between the horns,
which had been filed to a needle point. "Still goin' through with it?"
"Yaaaa," the bull lowed. "Yaooo kuhl Daan. Err'll kuhl uhhh kuhlerrs."
His intelligence was the result of atomic bombs and mutations
"The scientists got real excited when they heard about it, 'cause they
wanted to see how horrible they could make Atomic Bomb. So, they
shipped fifty-nine cattle up to Oak Ridge. That was a Government town,
a hundred miles southwest of here, where they made some of the stuff
to put in Atomic Bomb. The University of Tennessee was runnin' an
experimental farm there. They had donkeys, and pigs, and chickens, and
other animals that they exposed to radioactivity. Then they killed 'em
and cut 'em up to see what had happened. I know it's gruesome, but
that's how it was.