Sheep grazed on the White House lawn during the Wilson administration (1913-1921) as part of an effort to cut down on groundskeeping costs (and here and here). The photo above was taken by Harris & Ewing. Since there are lambs, I believe this is early spring.
The below photos were taken by the National Photo Company (all images via the Library of Congress Prints and Photographs Division).
Earlier, from 1910 to 1913, President Taft’s cow, Pauline, had grazed on the lawn. She is shown here in front of the Old Executive Office Building, then the State, War, and Navy Building.