As the first World War evoluated to a static war (in trenches and fortress lines) horses were less used for military objectives weren't they? After the lines for infrastructural duties and so; and perhaps in the second World War too. I do remember the last charge of the Polish lancers on the German tanks (if it's not entirely an urban legend), but were cavalry units used in any significant numbers on the battlefields after '18?

Ah yeah...the Russians...