Horse & Pony Books:
THE BURRO TAMER
(RANDOM HOUSE [USA] 1946)
ILLUSTRATED BY MANNING DE V. LEE
SUMMARY: Ricardo rescues a little burro from quicksand and hopes to train him to saddle.
CHEE AND HIS PONY
(HOUGHTON MIFFLIN [USA] 1950)
ILLUSTRATED BY WILLIAM MOYERS
SUMMARY: The Navajo boy Chee returns to the reservation from school hoping to find the pony his grandpa has promised him, but he is disappointed when no pony awaits him.
Fairly easy to find in the USA. A lot harder elsewhere.