Final answer:
The first National Vocational Dairy Cattle Judging Contest took place at the National Dairy Show in Chicago, forming the basis for FFA's Career Development Events. Chicago's Union Stockyards were symbolic of the livestock industry, which underwent changes in the mid-1900s due to technological advances in transportation and refrigeration.
Step-by-step explanation:
The first National Vocational Dairy Cattle Judging Contest was held at the National Dairy Show in Chicago, IL, which is notably recognized for its historical Union Stockyards. This particular contest provided a foundation for students of vocational agriculture to engage in practical assessment of livestock, which later evolved into the FFA's Career Development Events, a cornerstone for youth in agriculture education programs to develop their judging and vocational skills.
The context of the Union Stockyards in Chicago serves as a backdrop to this development in agricultural education. Dating back to 1947, the Stockyards were central to the livestock industry, particularly for cattle. However, due to advances in transportation and refrigeration, as mentioned in the source from the Library of Congress, urban feedlots began to decline by the mid-20th century. This historical shift underscores the importance of vocational education in adapting to the changes within the agricultural sector.