Our First Pony
This book was by the author of Misty series, King of the Wind, and Justin Morgan had a Horse. It is about a pair of twins that buy a pony and enter a show they got last place so they went home to call the doctor.
The doctor came and said that the pony was getting a baby and not just one but two. The day of birth one of the twins was too weak to get milk so they had to figure out how to save the baby...
READ TO FIND OUT WHAT HAPPENS TO THE FOAL!From Amazon:
Joseph and Justin may be twins, but they sure aren't much alike. Besides looking different, they live in very different worlds. Joseph loves the outdoors, the sky and the land, and all the animals, Justin, on the other hand, would rather be indoors, playing his piccolo or reading a book. The only thing they have in common is Midge, a pinto Shetland pony. They give her all the love and attention any pony could ever ask for. And she ends up giving them more than they ever could have imagined -- a horse family of their own!
With characteristic charm and simplicity, Marguerite Henry weaves a true-to-life tale about the joys and difficulties of owning and raising horses.