T H E work of livestock improvement has been coterminous with domesticated livestock husbandry almost from its beginnings. It has throughout most of its history proceeded so slowly that its progress has been barely perceptible from one generation to another. At times, however, when the enthusiasm of science or the driving force of high profit has been a sufficient motive, the livestock breeder has made conscious, and often rapidly fruitful, efforts to bring his animals closer to his ideal. The heydays of Grecian and Roman farming, monastic sheep husbandry in Britain in the Middle Ages, the great days of the Mesta in Spain, the period of high industrialism in the Low Countries in late mediaeval times, were all eras of stock improvement pursued at a high pitch. Beside the work of the men of vision, ambition and avarice which marked out these periods as phenomenal, there ran the patient, unchronicled and relatively modest achievements of a host of minor improvers; but, meritorious as these achievements often were, they had only a local significance. They brought to the hand of breeders in a small corner of a county somewhat better stock than they had had before.