This past weekend my son and I participated in a anti-fur protest and one of our fellow protestors gave me a copy of a film called "Earthlings". Although the film does not focus specifically on our use of and relationship with horses, they are included and discussed with a variety of other animals with whom we co-habitate with here on earth. It was produced in 2007 and is narrated by the actor Joaquin Phoenix.
If you are interested in educating yourself and your family about how humans treat our fellow species and how it is impacting our environment and health this is an excellent film. I caution that it is not for everyone, it will make you cry and you may never want to eat meat or fish again, wear leather, or continue to "look the other way" and ignore what is going on with our so-called food supply, clothing industry and entertainment industry. It will probably give you a few nightmares and I would never show it to young children who do not have the skills to deal with the graphic nature of the film.
If you are interested in viewing the film and can not find a free copy of it from a local animal rights organization chapter, send me an PM and I will make sure a copy gets sent to you.