Eric Hatch (1901-1973)
American author, staff writer on The New Yorker and also screenwriter. Born in 1901 in New York City. He was in addition an expert horseman, steward and show judge.
His horsy experience was to provide fodder for a humourous horse story, which was his most famous contribution to the genre. It was a very popular book and was made into a Disney film in 1968 entitled The Horse in the Gray Flannel Suit, although the film does not seem to have been as well-received as the book. The book itself was originally written as an adult story but was also marketed to the younger reader.
Eric Hatch also wrote another humourous adult novel called Spendthrift in which horses appear. It too was made into a film starring a very young Henry Fonda. Both the story and film are about a horse-loving playboy's romance with a stable-girl.
Hatch wrote many other novels, short stories and screenplays for a number of films and TV shows, as well as some non-fictional riding/horse care manuals. I am not sure if horses appeared in anything else, so if anyone knows please drop me a line!