You may or may not have seen this, but here is the last (at least I believe so) horse cavalry field manual put out by the US Army in 1941. There is some goodness in here as it reflects some thinking in how horses would be employed on the same battlefield as armor. Keep in mind though that its authors were also seeking to justify the continued use of horsed cavalry.
http://www.cgsc.edu/carl/docrepository/FM2_15.pdf