If you focus on the moving object the foreground and background will be appear to be blurred in the plane that the motion is happening.
In this painting I attempted to recreate this effect.
After some consideration I felt that I would use horizontal strokes throughout the foreground and background. This gives the entire painting a feeling of moving along a horizontal point. By not doing the same thing with the horses it brings them into sharper focus and makes them pop against the background.
A dusting of pastel powder to simulate mist helps to soften the effect, making it less pronounced and more realistic.