The exploitation of the herbage by means of the herbivora is a most ancient process. It seems at first sight that special nutritional problems are not involved, since flocks and herds are kept under conditions approximating very closely to the original environment of their species. In comparatively recent years, however, masses of herbivora have been in some cases either confined so that their range is greatly limited from that of their widely-grazing forbears, or transferred bodily to grasslands previously uninhabited by them, or transformed by the skill of breeders into creatures with a much higher output, and in consequence, a much higher intake. These novel factors have produced problems of their own which are not yet solved, though they have been, with some success, tackled by the practical man largely by empirical methods.