Matt, Mal & Julian, many thanks for your kind comments.
According to the exif data, it was 1/13th sec at f4, and 12mm on a Tokina 12-24mm. There was a 0.9 ND Grad on the lens, and the B&W conversion was done in Dynamic Photo HDR using only the B&W mixer, with some levels and tinting in Corel PSP.
It really was pure luck, hand held, spur of the second and hope for the best. The horses were 'grazing' rapidly towards me, and seconds later it was all soft muzzles and warm breath. I can't believe that the only serious blurring is the tail of the pony on the right.