Secretariat: The Making of a Champion by William Nack
Published 2002 by Da Capo Press (first published 1975)
Original title: Big Red of Meadow Stable
Added 5/5/11.
I did not read this book, but I saw the movie:
MOVIE: "Secretariat" (2010)
Stars: Diane Lane, John Malkovich and Margo Martindale
http://www.imdb.com/title/tt1028576/
http://movies.netflix.com/Movie/Secre...
"Penny Chenery Tweedy and colleagues guide her long-shot but precocious stallion to set, in 1973, the unbeaten record for winning the Triple Crown."
"The film explores Chenery's bond with "Big Red" and depicts her rise to greatness as the 'first lady of racing.'"

FACTS ABOUT THE TRIPLE CROWN:
Secretariat won the Triple Crown in 1973.
In the United States, the three races that compose the Triple Crown are:
1. Kentucky Derby - at Churchill Downs in Louisville, Kentucky;
2. Preakness Stakes - at Pimlico Race Course in Baltimore, Maryland
3. Belmont Stakes - at Belmont Park in Elmont, New York.
"The Triple Crown of Thoroughbred Racing ...consists of three races for three-year-old Thoroughbred horses. Winning all three of these Thoroughbred horse races is considered the greatest accomplishment of a Thoroughbred racehorse."
Lists of past Triple Crown winners can be found at:
http://en.wikipedia.org/wiki/Triple_C...

FACTS ABOUT SECRETARIAT:
"Secretariat's genetic legacy may be linked in part to the likelihood that he carried the "x-factor", a trait linked to a large heart, carried only on the x-chromosome, and thus, a trait that Secretariat could only pass on via his daughters.
"[After Secretariat's death in 1989, at the age of 19] a necropsy [i.e., autopsy] revealed that his heart was significantly larger than that of an ordinary horse. ... [It was] estimated that Secretariat's heart probably weighed 22 pounds or about two-and-a-half times as large as that of the average horse."
FROM: http://en.wikipedia.org/wiki/Secretar...

NOTE: Another non-fiction book about horses was _Seabiscuit_. See my review at:
http://www.goodreads.com/review/show/...