Tomorrow, The Discovery Channel's shameless annual sharkfest kicks off. This does not constitute a significant cross-over with horse books, as horses generally stay on land. However...
... didn't you just know the exception to the shark/horse rule would be Walter Farley? Sharks menace Tena in The Horse That Swam Away and nearly eat Alec (once again shipwrecked) in The Black Stallion and Flame. In the latter book, the Black is also attacked by a vampire bat, pictured above on the 1970's paperback cover looking as big as a turkey vulture.
Anyone want a contest where you can win vintage (cough) horse books? I have some rattling around that I keep meaning to do a contest for, but I wasn't sure if anyone would be interested. I mean, these are books you can get at Amazon for a penny. On the plus side, they'd be free and the only requirement to enter would be a comment on future reviews.
Also, I once reviewed a picture book, Horses by Blanche Chenery Perrin. Recently, I came across a comics blog which shows the entire (well, it was a Little Golden Book) book. Well worth a look - I really like Hamilton Greene's illustrations.