 In 1878 , the British organization now known as the Shire Horse Society was created , with the American Shire Horse Association beginning in 1885 . The breed was exported from Britain to the United States in large numbers during the late 19th and early 20th centuries , but popularity fell as mechanisation increased , reaching a low point in the 1950s and 1960s . Popularity began to increase again in the 1970s and after . However , population numbers are still considered to be at critical levels by both the UK @-@ based Rare Breeds Survival Trust and the US @-@ based American Livestock Breeds Conservancy . 
