That in the winter of 1836/37 my great-great-great grandfather's horses produced dung which was "pale, clay-like, and fetid".
ETA: he operated a coach service between Glasgow and Edinburgh (4 1/2 hours journey time, fare 5s outside, 10s inside), so kept horses. In that winter there was a shortage of hay, so he used wheat straw, with the resulting change in dung. For more details see Stable Economy: A treatise on the management of horses, in relation to stabling, grooming,feeding, watering, and grooming by Professor John Stewart, published 1845.