There is a book I read many years ago called "Jack"...I have the book somewhere at home, but right now cannot locate it...and unfortunately cannot recall the author's name. It was written several years ago, and is a fictional story of a young man in England who helps out on a neighbor's farm, taking care of the horses. One of the horses, Beth, is a heavy horse - Clyde, if I remember correctly - and Jack has formed a very strong bond with her. When the horses are taken by the government to be used to pull weapons carts in the war, Jack becomes distraught, and finally enlists in the army so he can go and find his beloved Beth and bring her home.
It's a heartwrenching story, very well written...and I think it would make a perfect movie.