Fantasy Friday: A High Turn-Over Rate Explained

O'Liam spent his days upon high plains
Beneath the purest skies, the brightest sun.
He filled his canteen at streams fed by rains
The gods themselves had sent. When day was done
He played his pipes then slept in starlight, glad
And merry. All was happiness until
Roe Rippon met his end, and met it bad.
This left a vacancy for Li to fill.
The herd was wondrous, beauty on the hoof,
Each mare of shining whiteness that would blind
Mere laymen's eyes. But those who called the Roof
Of Mountains home, were chosen. All was fine.
But then a stallion found the herd. Li failed
To fend him off, and, like Roe, died impaled.