Final answer:
The first National Vocational Dairy Cattle Judging contest was held in 1925 at Chicago's Union Stockyards, a key location for livestock commerce at that time.
Step-by-step explanation:
The first National Vocational Dairy Cattle Judging contest took place in 1925 at the Union Stockyards in Chicago, IL. The contest was part of the vocational education movement and agricultural education, and it provided an opportunity for students to showcase their skills in dairy cattle evaluation. This tradition allowed students to learn and apply their knowledge in a competitive setting. The Union Stockyards were a central hub for agricultural commerce during that time and were an iconic location for such an event, especially given the site's historical significance within the meat packing and livestock industry, as explained by the provided source which describes the Stockyards' operations in 1947. Although advances in transportation and refrigeration eventually led to the decline of the urban feedlots by the mid-1900s, the legacy of agricultural skills competitions like dairy cattle judging continues today.