Stocking and overstocking are clearly relative terms. The number of animals a definite area of land will carry will of course depend upon the fertility of the soil and its power of sustaining growth through the year, as well as upon the nature and character of the herbage it produces. Horses have a strong predilection for the finer grasses, and from a grazing point of view may be regarded as wasteful feeders. Nothing is more striking than the way in which they will clear the grass off certain patches down to the roots, and continue to graze the ground over again and again, while other parts of the pasture are covered with a luxuriant growth which they altogether neglect. Acreage, therefore, is no absolute measure of the sustaining power of pasture land, but rather the quantity and quality of suitable herbage it produces. It is on account of this residue of rough grass that bullocks prove so useful after horses. They eat off the coarse herbage, and lay bare a fresh succulent bite which horses will attack when there is a shortage of the better kinds.
Among other reasons, it is this partiality to certain parts of pastures which has rendered it desirable to provide a large area of ground for horses to run over. In a pamphlet published by Sir Walter Gilbey on Young Racehorses, it is pointed out that " one yearling to every five or six acres is plenty ".
Nothing tends so much to the deterioration of pasture land as overstocking with horses. By this is not to be understood the mere placing on it of more horses than it can fairly carry and support, but grazing it year after year without intermission or association with cattle. By this method of treatment the fine herbage becomes less abundant and the coarse rejected variety, remaining to seed, is more largely distributed.
Moreover, if wet or boggy as a whole or in parts, the soil becomes foul, and serves as a suitable environment for the growth and maturation of the larvae of equine parasites, which, when once introduced, continue to multiply year by year, invading first one animal and then another, until under favourable conditions the great bulk of the breeding-stock become more or less severely infected.
Poverty, stunted growth, infertility, and abortion are among the consequences of this too common mismanagement. Land devoted to horse-breeding should be periodically grazed with cattle or mown for hay, and, save on limestone or chalk formation, should be subjected to a good dressing with lime and salt.