Southdown sheep no longer economical and smaller flocks averaged only 135 ewes apiece. The use of artificial fertilizers had gained ground, and the combine-drill, which sowed grain seeds and fertilizer together, rendered close-folding by sheep unnecessary. Gradually surrendering to basic arable farming changes, the Southdown became largely a grassland breed. During the interwar years, the United Kingdom was known for farm animal breeding, and pedigreed Southdowns were still being exported to most parts of the world, especially New Zealand. In 1937, the number of exported Southdowns reached 459 head. During the Great Depression, a severe and prolonged fall in the prices of
Breed registry conformation shows. For the breed to move to the Miscellaneous class and then to fully recognized status, the breed's stud book must be closed. A closed stud book allows the breed to stay very pure to its type, but limits its ability to be improved. This may put a breed at a disadvantage, especially in performance disciplines, where an animal is worth more if it is successful in competition even if it is not pure. It also limits the gene pool, which may make certain undesirable characteristics become accentuated in the breed, such as a poor conformational fault or a