I am thinking it was something to do with the King Ranch in Texas...?
The King Ranch was started in the mid 1850s and is well known for their breeding program of cattle and quarter horses.
They developed the Santa Gertrudis cattle breed --
http://www.king-ranch.com/operations...nta-gertrudis/
http://www.king-ranch.com/operations...-improvements/
But I am not sure of a book about their breeding program and would also be interested in what the book title would be?